CHAPTER III STATIC ELECTRIC MACHINESA Cylinder Electric MachineThe electrophorus described in the last chapter is capable of furnishing sufficient electricity for many interesting experiments, but for the purpose of procuring larger supplies of electricity, a static electric machine is necessary.An electric machine is composed of two parts, one for producing the electricity by the friction of two surfaces rubbing against each other, and the other an arrangement for collecting the electricity thus formed.The earliest form of electric machine consisted of a ball of sulphur fixed upon a spindle which could be rotated by means of a crank. When the dry hands were pressed against the sulphur by a person standing on a cake of resin, which insulated him, sparks could be drawn from his body.Later a leather cushion was substituted for the hands, and a glass cylinder for the ball of sulphur, so that the frictional electric machine now consists of a cylinder or a disk of glass mounted upon a horizontal axis capable of being turned by a handle. A leather cushion, stuffed with horsehair and covered with a powdered amalgam of zinc or tin, presses against one side of the cylinder. A "prime" conductor in the shape of an elongated cylinder presents a row of fine metal spikes, like the teeth of a rake, to the opposite side. A flap of silk attached to the leather cushion passes over the cylinder and covers the upper half.Fig. 29.—Front View of a Cylinder Electric Machine.Fig. 29.—Front View of a Cylinder Electric Machine.When the handle of the machine is turned, the friction produced between the leather cushion and the glass generates a supply of positive electricity on the glass, which is collected, as the cylinder revolves, by the row of sharp points, and transferred to the prime conductor.The first thing required in the construction of an electric machine is a large glass bottle having a capacity of from two to four quarts.The insulating power of glass varies considerably. Common green glass (not white glass colored green by copper, but glass such as the telegraph insulators are made from) generally insulates the best. Some sorts of white glass, the Bohemian especially, are good insulators, but this quality will not usually be found in ordinary bottles.Fig. 30.—Method of Finding the Center of a Circle.Fig. 30.—Method of Finding the Center of a Circle.Select a smooth bottle which has no lettering embossed upon it, and stand it upon a piece of white paper. Trace on the paper a line around the circumference of the bottle so that the circle thus formed is of the same size as the bottom of the bottle. Lay a carpenter’s square on the circle so that the pointCjust touches the circumference. Draw a line fromAtoBwhere the sides of the square cut the circumference. The point in the middle of this line is the center of the circle.Place the paper on the bottom of the bottle so that the circle coincides with the circumference, and mark the center of the bottle.The bottle must now be drilled. This is accomplished with a small three-cornered file, the end of which has been broken off so as to form a ragged cutting edge. The file is set in a brace and used like an ordinary drill. During the boring process the drill must be frequently lubricated with a mixture of gum camphor and turpentine. The drilling, which will require almost an hour before the glass is pierced, if the bottle is a thick one, should be performed slowly and carefully, so as to avoid all danger of cracking the glass. The hole, when finished, should be from one-quarter to three-eighths of an inch in diameter.After the hole has been bored, fit a wooden plug into the neck of the bottle and cement it there with a mixture composed of one-half a pound of resin, five ounces of beeswax, one-quarter of an ounce of plaster of Paris, and three-quarters of an ounce of red ocher, melted together over a moderately warm stove. Dip the plug in the molten cement and force it into the neck of the bottle. When the cement dries it will be impossible to remove it.The sizes of bottles vary, so that it is quite impossible to give dimensions which must be closely followed in constructing the machine. Those in the text are approximate. The drawings have been made to scale so as to show the proportions the parts bear to each other.A heavy wooden base will be required to mount the machine on. Two uprights are mounted on the base to support the axis of the bottle. Through one of these bore a hole of the same diameter as the wooden plug fitted in the neck of the bottle. The end of the wooden plug projecting through the upright is notched and fitted with a crank so that the bottle may be revolved. The handle of the crank is an ordinary spool having one flange cut off and mounted with a screw and a washer.Fig. 31.—The "Rubber."Fig. 31.—The "Rubber."The machine is now ready for the "rubber" and "prime conductor." The rubber is a piece of wood one inch square and from six to eight inches long. A piece of undressed leather is tacked on as shown in the illustration and stuffed with horsehair. The wood is shellacked and covered with tin-foil previous to tacking on the leather. A strip of wood, two inches wide and one-half an inch thick, is fastened to the back of the rubber. The strip should be just long enough so that when the lower end rests on the base the rubber is level with the axis of the bottle. The lower end may be fastened to the base by means of a small brass hinge. Two rubber bands stretch from hooks between the rubber and the base so as to pull the former tightly against the bottle. The illustration shows a method of mounting the rubber on a foot-piece held to the base with a thumb-nut so that it may be slid back and forth and the pressure varied at will.The prime conductor is formed from a piece of curtain-pole two inches in diameter and eight inches long. The ends are rounded with a rasp and then smoothed with sandpaper. The whole surface is then shellacked and covered with a layer of tinfoil. The heads of a number of dressmaker’s pins are cut off, and the pins forced into the side of the prime conductor with a pair of pincers. They should form a row like the teeth of a rake about three-eighths of an inch apart. A hole is bored in the center of the under side of the prime conductor to receive a glass rod one-half inch in diameter. A second hole of the same size is bored in the base in such a position that when the glass rod is in place, the teeth on the prime conductor are on a level with the axis of the bottle, and their points about 3-32 of an inch away from the glass. The glass rod must be used in order to insulate the prime conductor and prevent the escape of the electricity. It is secured with some of the cement described on page 33. A piece of water-gauge glass may be used in place of a glass rod.Fig. 32.—The Prime Conductor or Collector.Fig. 32.—The Prime Conductor or Collector.A strip of oiled silk, or in its place a strip of silk which has been shellacked, eight or nine inches wide, and long enough to reach half-way around the bottle, is tacked to the rubber so that the silk covers the upper half of the cylinder and comes over to within one-quarter of an inch of the steel points.The machine is now complete, and when the handle is turned rapidly, you will be able to draw sparks from the prime conductor. The sparks will probably be very short, about one-half of an inch long. These can be increased, however, to three inches, if the glass is of the right quality, by treating the rubber with amalgam.The amalgam is formed by melting one ounce of tin and adding to it one ounce of zinc in small bits. As soon as the zinc has also melted add to the mixture two ounces of mercury which has been previously warmed. Be careful not to inhale any of the vapor during this operation. Pour the mixture into a vessel of cold water, which will reduce the metal to small grains. Pour off the water and grind the amalgam to a powder by pounding the grains with a hammer.The leather rubber should bethinlysmeared with lard and the powdered amalgam rubbed on it.In order to obtain the greatest effect from an electric machine, it must be carefully freed from dust and particles of amalgam adhering to the glass, and the insulating column rubbed with a warm woolen cloth. The best results are obtained by placing the machine near a stove or radiator where it is warm.Fig. 33.—The Complete Cylinder Electric Machine.Fig. 33.—The Complete Cylinder Electric Machine.A Wimshurst MachineThe Wimshurst Machine consists of two varnished glass plates revolving in opposite directions. On the outside of each of these plates are cemented a number of tinfoil "sectors," arranged radially. Two conductors at right angles to each other extend obliquely across the plates, one at the back and the other at the front. These conductors each terminate in brushes of tinsel which electrically excite the "sectors" as the plates revolve. The electricity is collected by a set of "collectors" arranged in a somewhat similar manner to the collector on the cylinder electric machine.The Glass Platesare each eighteen inches in diameter. Purchase two panes of clear glass twenty inches square from a glass dealer. The white glass is far preferable to the green glass and will make the best electric machine. The plates should be of the thickness known as "single light" and should be perfectly free from wavy places, bubbles, or other imperfections.Fig. 34.—Paper Pattern for laying out the Plates.Fig. 34.—Paper Pattern for laying out the Plates.The work is first laid out on a piece of stiff paper twenty inches square as a pattern. Describe a circle four inches in diameter. Using the same center, draw other circles, making them respectively eight, sixteen, and eighteen inches in diameter. Then mark sixteen radial lines, from the center, making them equal distances apart, as shown in Figure 34.Fig. 35.—Plate with Sectors in Position, and a Pattern for the Sectors.Fig. 35.—Plate with Sectors in Position, and a Pattern for the Sectors.Lay one of the glass panes over the pattern and cut out a glass circle eighteen inches in diameter, or perhaps you may be able to have a glazier do the cutting for you and so save considerable trouble and possible breakage. Two such plates should be made.The Sectors are cut from heavy flat tinfoil according to the pattern shown in Figure 35. They should be made one inch and one-half wide at the wide end and three-quarters of an inch at the other end. They are each four inches long. Thirty-two such sectors are required. The easiest way to make them is to cut out a pattern from heavy cardboard to serve as a guide.Clean and dry both of the glass plates very carefully and then give them each two thin coats of white shellac. After they have been dried, lay one of the plates on the paper pattern so that the outside of the plate will coincide with the largest circle on the paper.Then place a weight in the center of the plate so that it will not move, and stick sixteen of the tinfoil sectors on the plate with thick shellac. The sectors are arranged symmetrically on the plate, using the eight-inch and sixteen-inch circles and the radial lines as guides. Both plates should be treated in this manner. Each sector should be carefully pressed down on the glass, so that it will stick smoothly without air-bubbles or creases. When all the sectors are in place the plates will appear like that shown in Figure 35.The Bosseswill have to be turned out at a wood-working mill or at some place where they have a turning-lathe. The bosses are four inches in diameter at the large end and one inch and one-half at the other. A groove is turned near the small end of each to accommodate a round leather belt.A hole should be made in each boss about half-way through from the small end. These holes should be bushed with a piece of brass tubing having an inside diameter of one-half inch. The tubing should go into the hole very snugly and be a "driven fit."Fig. 36.—A Side View of one of the Bosses, showing the Brass Bushing used.Fig. 36.—A Side View of one of the Bosses, showing the Brass Bushing used.The bosses should both be given a coat of shellac, and after this is dry, fastened to the glass plates on the same side to which the tinfoil sectors are attached. The best plan is to lay the disks on the paper pattern and adjust them until the outer edge coincides with the largest circle.Then apply somebichromate glueto the flat surface of one of the bosses and place the latter in the center of the plate in line with the smallest circle.Place a weight on the boss to hold it down firmly against the plate and leave it over night, or for ten or twelve hours, until thoroughly dry.The glue is prepared by placing some high-grade glue in a tin cup and covering it with cold water. Allow it to stand until the glue absorbs all the water it will and becomes soft. Then pour the water off and add enoughglacial acetic acidto cover the glue.Heat the mixture until it is reduced to a liquid, stirring it until it is perfectly smooth. Add a teaspoonful of powdered bichromate of potash to the glue.The glue must now be kept in the dark, for sunlight will "set" the glue so that it becomes insoluble.The Frame of the machine is composed of two strips twenty-five inches long, three inches wide, and an inch and one-half in thickness, and two cross-pieces of the same thickness and width fifteen inches long.Fig. 37.—The Frame.Fig. 37.—The Frame.Notches are cut at both sides of the base to admit the feet of the uprights.The Uprightsare seventeen inches long, three inches wide, and one and one-half inches thick.Fig. 38.—The Upright.Fig. 38.—The Upright.The notch at the foot is cut the same width as the thickness of the long members of the frame and is arranged so that when fitted in place, the foot of the upright will rest on the table in line with the bottom of the cross-pieces.The Driving-Wheelsare turned out of wood on a lathe. They are seven inches in diameter and seven-eighths of an inch thick. A groove should be turned in the edge to carry a small round leather belt. The wheels are mounted on a wooden axle made from a round curtain-pole. They are glued to the axle and arranged so that the grooves will fall directly underneath the pulleys turned in the bosses.Fig. 39.—The Driving-Wheels and Axle.Fig. 39.—The Driving-Wheels and Axle.The ends of the axle pass through the uprights, five inches above the bottom.The front end of the axle is fitted with a crank and a handle.Fig. 40—The Boss and Axle. For sake of clearness, the Plate is not shown.Fig. 40—The Boss and Axle. For sake of clearness, the Plate is not shown.The plates are mounted on short iron axles passing through the top of the upright into the brass bushings. One end of each of the axles is filed flat where it passes through the wood upright so that it may be firmly held by a set-screw and prevented from revolving.Fasten a small fiber washer to the center of one glass disk so that it will separate the plates and prevent them from touching when revolving.The collectors, quadrant rods, etc., are mounted on glass rods one inch in diameter. The bottoms of the rods fit in holes (H H) bored in the cross-pieces of the base, Figure 37. The upper ends are each fitted with a brass ball two inches in diameter. The balls are mounted on the rods by soldering a piece of brass tubing to the ball and slipping it over the rod. The rods should be of the proper length to bring the center of the balls on a line with the center of the plates.Fig. 41—Showing how the Ball, Comb, etc., are mounted on the Glass Rod.Fig. 41—Showing how the Ball, Comb, etc., are mounted on the Glass Rod.Make two forks as shown in Figure 42 out of brass rod, three-sixteenths of an inch in diameter and solder brass balls at the ends. The forks are eleven inches long.A number of small holes must be bored in the "prongs" and pins made by cutting ordinary dressmakers’ pins in half and soldering them in place. These pins, mounted on the forks, form the combs or collectors.Bore a horizontal hole through each of the brass rods on the top of the glass rods and pass the shanks of the forks through and solder them in place.One of the shanks may be provided with a discharge ball at the end as shown byD Bin Figure 44. The other is provided with a hard rubber handle made from a piece of rod. Bore a three-eighths hole directly in the top of each brass ball to receive the quadrant rods forming the spark-gap.Fig. 42.—A Comb or Collector.Fig. 42.—A Comb or Collector.The quadrant rods extend over the top of the plates and are three-eighths of an inch in diameter. They are loose in the tops of the balls so that they may be moved about or removed entirely.A small brass ball three-quarters of an inch in diameter should be soldered to the top of one of the quadrant rods and a similar ball two inches in diameter to the other.Fig. 43.—Showing how the Tinsel Brushes are arranged on the "Neutralizer" Rods.Fig. 43.—Showing how the Tinsel Brushes are arranged on the "Neutralizer" Rods.Two large brass balls, two inches in diameter, are fitted over the ends of the axles, which project through the uprights. Bore a one-quarter-inch hole through each ball at right angles to the axle and slip a one-quarter-inch brass rod through and solder it fast.Fig. 44.—The Complete Wimshurst Electric Machine.Fig. 44.—The Complete Wimshurst Electric Machine. B B B B,Brushes. C C,Combs. D B,Discharge Ball. I I,Glass Rods. H,Handle. Q Q,Quadrant Rods. S S S S S,Sectors. S G,Spark-Gap. P P,Driving-Wheels. For the sake of clearness, several of the sectors are not shown.The ends of the rods should be tipped with a bunch of tinsel or fine copper wires and be curved so that the brushes so formed will just touch the sectors on the disks when the latter are revolved.These are the neutralizers and are arranged in the approximate positions shown in Figure 44.The driving-wheels are connected to the bosses by means of small round leather belts. The belt at the rear of the machine is crossed in order to make the plates revolve in opposite directions.If the machine has been properly built it is now ready for operation. It may be necessary to charge the machine the first time that it is used by touching several of the sectors with the charged cover of an electrophorus. Then if the handle is turned the accumulated electricity should discharge across the spark-gap at the top of the machine in the form of bright blue sparks.Experiments with an Electric MachineMany interesting experiments can be performed with an electric machine. The number is almost unlimited. A few of the most instructive ones are described below. Others can be found in almost any text book on physics.The Leyden jarconsists of a glass jar coated with tinfoil part way up on both the outside and inside. Through the wooden stopper passes a brass rod or a heavy copper wire which connects with the inner coating of tinfoil by means of a small brass chain. The upper and outside end of the rod usually terminates in a brass ball or knob.It is a very simple matter to make a good Leyden jar.Fig. 45.—The Leyden Jar.Fig. 45.—The Leyden Jar.The jar must be thoroughly cleaned and dried before coating. The inside is then given a thorough brushing over with shellac or varnish. Before it is dry, carefully insert the tin-foil and press it smoothly against the glass. The outside of the jar is treated and coated in the same manner. The inside and outside of the bottom are also coated by cutting the tinfoil in circular pieces and shellacking them on.In order to charge the Leyden jar, grasp it in the hand near the bottom and hold the knob against the prime conductor while turning the handle of the machine.Fig. 46.—A Wooden Mortar for Igniting Gunpowder.Fig. 46.—A Wooden Mortar for Igniting Gunpowder.Igniting gunpowder.Bore a hole one-half inch in diameter and one inch deep in a block of hardwood. Pass two small brass wires through holes in the sides, letting the ends of the wires be about one-eighth of an inch apart. Pour a little gunpowder in loosely over the wires. Tie a piece of thoroughly moistened cotton twine, three inches long, to one of the wires and attach it to the outside coating of a charged Leyden jar.Connect the knob of the jar to the other wire. The gunpowder will immediately explode. Keep the face and hands away from the gunpowder when performing this experiment.Fig. 47.—An Electric Umbrella.Fig. 47.—An Electric Umbrella.Electric Umbrella.The repulsion of similarly electrified bodies which was illustrated by the action of the pith ball electroscope may be better illustrated by pasting some narrow streamers of tissue paper about one-eighth of an inch wide and four inches long to a small cork covered with tinfoil. The cork is mounted on the upper end of a stiff copper wire supported in a bottle. When the wire is connected to the prime conductor and the machine set in motion, the strips will spread out like an umbrella.Lightning Board.A pane of glass is thoroughly cleaned and then given a coat of shellac or varnish. Before the varnish is dry, press on a piece of tinfoil large enough to cover one side of the glass and rub it down smoothly.Fig. 48.—A Lightning Board.Fig. 48.—A Lightning Board.After the shellac or varnish is dry, cut the tinfoil up into innumerable little squares with a sharp knife and ruler, leaving two solid strips of tinfoil at the ends of the glass pane.The pane is mounted by cementing it in a slot in the cork of a bottle. Connect one of the tinfoil strips to the prime conductor and the other to the earth or the body. When the machine is turned, innumerable little sparks will pass between the tinfoil squares and give an appearance very similar to that of lightning.Fig. 49.—An Electric Dance.Fig. 49.—An Electric Dance.The Electrical Dance.A number of little balls of cork or pith are enclosed in a cylinder of glass about two and one-half or three inches high formed by cutting off the top of a lamp chimney. The top and bottom of the cylinder are closed by two circular pieces of sheet brass or copper. The top disk is connected to the prime conductor while the bottom one is connected to the rubber. When the machine is set in motion, the little balls will dance up and down. Bits of feather or paper cut to represent figures of men and women may be used as well as pith or cork balls.The Electric Whirl.The whirl consists of an S shaped piece of brass wire, pointed at both ends and supported on a needle by a little conical depression made in the center with a punch.Fig. 50.—An Electric Whirl.Fig. 50.—An Electric Whirl.The needle is stuck in a cork in the top of a bottle and connected with the prime conductor of the electric machine. When the latter is set in motion, the whirl will commence to revolve at a high rate of speed.Lichtenberg’s Figurescan be produced by charging a Leyden jar by connecting the knob or inside coating with the prime conductor and holding the outside coating in the hand.Then trace a small circle on the electrophorus bed with the knob.Charge a second Leyden jar by connecting the outside coating with the prime conductor.The inside coating should be connected to the rubber by means of a wire fastened to the knob. The same result may be obtained by connecting the outside coating with the prime conductor and touching the knob with the hand.Then trace a cross on the electrophorus bed with the knob, making the cross inside of the circle.Fig. 51.—Lichtenberg's Figures.Fig. 51.—Lichtenberg's Figures.Shake a mixture of red lead and sulphur through a muslin bag from a height of several inches over the electrophorus.The red lead will accumulate around the cross and the sulphur around the circle.CELLS AND BATTERIES
CHAPTER III STATIC ELECTRIC MACHINESA Cylinder Electric MachineThe electrophorus described in the last chapter is capable of furnishing sufficient electricity for many interesting experiments, but for the purpose of procuring larger supplies of electricity, a static electric machine is necessary.An electric machine is composed of two parts, one for producing the electricity by the friction of two surfaces rubbing against each other, and the other an arrangement for collecting the electricity thus formed.The earliest form of electric machine consisted of a ball of sulphur fixed upon a spindle which could be rotated by means of a crank. When the dry hands were pressed against the sulphur by a person standing on a cake of resin, which insulated him, sparks could be drawn from his body.Later a leather cushion was substituted for the hands, and a glass cylinder for the ball of sulphur, so that the frictional electric machine now consists of a cylinder or a disk of glass mounted upon a horizontal axis capable of being turned by a handle. A leather cushion, stuffed with horsehair and covered with a powdered amalgam of zinc or tin, presses against one side of the cylinder. A "prime" conductor in the shape of an elongated cylinder presents a row of fine metal spikes, like the teeth of a rake, to the opposite side. A flap of silk attached to the leather cushion passes over the cylinder and covers the upper half.Fig. 29.—Front View of a Cylinder Electric Machine.Fig. 29.—Front View of a Cylinder Electric Machine.When the handle of the machine is turned, the friction produced between the leather cushion and the glass generates a supply of positive electricity on the glass, which is collected, as the cylinder revolves, by the row of sharp points, and transferred to the prime conductor.The first thing required in the construction of an electric machine is a large glass bottle having a capacity of from two to four quarts.The insulating power of glass varies considerably. Common green glass (not white glass colored green by copper, but glass such as the telegraph insulators are made from) generally insulates the best. Some sorts of white glass, the Bohemian especially, are good insulators, but this quality will not usually be found in ordinary bottles.Fig. 30.—Method of Finding the Center of a Circle.Fig. 30.—Method of Finding the Center of a Circle.Select a smooth bottle which has no lettering embossed upon it, and stand it upon a piece of white paper. Trace on the paper a line around the circumference of the bottle so that the circle thus formed is of the same size as the bottom of the bottle. Lay a carpenter’s square on the circle so that the pointCjust touches the circumference. Draw a line fromAtoBwhere the sides of the square cut the circumference. The point in the middle of this line is the center of the circle.Place the paper on the bottom of the bottle so that the circle coincides with the circumference, and mark the center of the bottle.The bottle must now be drilled. This is accomplished with a small three-cornered file, the end of which has been broken off so as to form a ragged cutting edge. The file is set in a brace and used like an ordinary drill. During the boring process the drill must be frequently lubricated with a mixture of gum camphor and turpentine. The drilling, which will require almost an hour before the glass is pierced, if the bottle is a thick one, should be performed slowly and carefully, so as to avoid all danger of cracking the glass. The hole, when finished, should be from one-quarter to three-eighths of an inch in diameter.After the hole has been bored, fit a wooden plug into the neck of the bottle and cement it there with a mixture composed of one-half a pound of resin, five ounces of beeswax, one-quarter of an ounce of plaster of Paris, and three-quarters of an ounce of red ocher, melted together over a moderately warm stove. Dip the plug in the molten cement and force it into the neck of the bottle. When the cement dries it will be impossible to remove it.The sizes of bottles vary, so that it is quite impossible to give dimensions which must be closely followed in constructing the machine. Those in the text are approximate. The drawings have been made to scale so as to show the proportions the parts bear to each other.A heavy wooden base will be required to mount the machine on. Two uprights are mounted on the base to support the axis of the bottle. Through one of these bore a hole of the same diameter as the wooden plug fitted in the neck of the bottle. The end of the wooden plug projecting through the upright is notched and fitted with a crank so that the bottle may be revolved. The handle of the crank is an ordinary spool having one flange cut off and mounted with a screw and a washer.Fig. 31.—The "Rubber."Fig. 31.—The "Rubber."The machine is now ready for the "rubber" and "prime conductor." The rubber is a piece of wood one inch square and from six to eight inches long. A piece of undressed leather is tacked on as shown in the illustration and stuffed with horsehair. The wood is shellacked and covered with tin-foil previous to tacking on the leather. A strip of wood, two inches wide and one-half an inch thick, is fastened to the back of the rubber. The strip should be just long enough so that when the lower end rests on the base the rubber is level with the axis of the bottle. The lower end may be fastened to the base by means of a small brass hinge. Two rubber bands stretch from hooks between the rubber and the base so as to pull the former tightly against the bottle. The illustration shows a method of mounting the rubber on a foot-piece held to the base with a thumb-nut so that it may be slid back and forth and the pressure varied at will.The prime conductor is formed from a piece of curtain-pole two inches in diameter and eight inches long. The ends are rounded with a rasp and then smoothed with sandpaper. The whole surface is then shellacked and covered with a layer of tinfoil. The heads of a number of dressmaker’s pins are cut off, and the pins forced into the side of the prime conductor with a pair of pincers. They should form a row like the teeth of a rake about three-eighths of an inch apart. A hole is bored in the center of the under side of the prime conductor to receive a glass rod one-half inch in diameter. A second hole of the same size is bored in the base in such a position that when the glass rod is in place, the teeth on the prime conductor are on a level with the axis of the bottle, and their points about 3-32 of an inch away from the glass. The glass rod must be used in order to insulate the prime conductor and prevent the escape of the electricity. It is secured with some of the cement described on page 33. A piece of water-gauge glass may be used in place of a glass rod.Fig. 32.—The Prime Conductor or Collector.Fig. 32.—The Prime Conductor or Collector.A strip of oiled silk, or in its place a strip of silk which has been shellacked, eight or nine inches wide, and long enough to reach half-way around the bottle, is tacked to the rubber so that the silk covers the upper half of the cylinder and comes over to within one-quarter of an inch of the steel points.The machine is now complete, and when the handle is turned rapidly, you will be able to draw sparks from the prime conductor. The sparks will probably be very short, about one-half of an inch long. These can be increased, however, to three inches, if the glass is of the right quality, by treating the rubber with amalgam.The amalgam is formed by melting one ounce of tin and adding to it one ounce of zinc in small bits. As soon as the zinc has also melted add to the mixture two ounces of mercury which has been previously warmed. Be careful not to inhale any of the vapor during this operation. Pour the mixture into a vessel of cold water, which will reduce the metal to small grains. Pour off the water and grind the amalgam to a powder by pounding the grains with a hammer.The leather rubber should bethinlysmeared with lard and the powdered amalgam rubbed on it.In order to obtain the greatest effect from an electric machine, it must be carefully freed from dust and particles of amalgam adhering to the glass, and the insulating column rubbed with a warm woolen cloth. The best results are obtained by placing the machine near a stove or radiator where it is warm.Fig. 33.—The Complete Cylinder Electric Machine.Fig. 33.—The Complete Cylinder Electric Machine.A Wimshurst MachineThe Wimshurst Machine consists of two varnished glass plates revolving in opposite directions. On the outside of each of these plates are cemented a number of tinfoil "sectors," arranged radially. Two conductors at right angles to each other extend obliquely across the plates, one at the back and the other at the front. These conductors each terminate in brushes of tinsel which electrically excite the "sectors" as the plates revolve. The electricity is collected by a set of "collectors" arranged in a somewhat similar manner to the collector on the cylinder electric machine.The Glass Platesare each eighteen inches in diameter. Purchase two panes of clear glass twenty inches square from a glass dealer. The white glass is far preferable to the green glass and will make the best electric machine. The plates should be of the thickness known as "single light" and should be perfectly free from wavy places, bubbles, or other imperfections.Fig. 34.—Paper Pattern for laying out the Plates.Fig. 34.—Paper Pattern for laying out the Plates.The work is first laid out on a piece of stiff paper twenty inches square as a pattern. Describe a circle four inches in diameter. Using the same center, draw other circles, making them respectively eight, sixteen, and eighteen inches in diameter. Then mark sixteen radial lines, from the center, making them equal distances apart, as shown in Figure 34.Fig. 35.—Plate with Sectors in Position, and a Pattern for the Sectors.Fig. 35.—Plate with Sectors in Position, and a Pattern for the Sectors.Lay one of the glass panes over the pattern and cut out a glass circle eighteen inches in diameter, or perhaps you may be able to have a glazier do the cutting for you and so save considerable trouble and possible breakage. Two such plates should be made.The Sectors are cut from heavy flat tinfoil according to the pattern shown in Figure 35. They should be made one inch and one-half wide at the wide end and three-quarters of an inch at the other end. They are each four inches long. Thirty-two such sectors are required. The easiest way to make them is to cut out a pattern from heavy cardboard to serve as a guide.Clean and dry both of the glass plates very carefully and then give them each two thin coats of white shellac. After they have been dried, lay one of the plates on the paper pattern so that the outside of the plate will coincide with the largest circle on the paper.Then place a weight in the center of the plate so that it will not move, and stick sixteen of the tinfoil sectors on the plate with thick shellac. The sectors are arranged symmetrically on the plate, using the eight-inch and sixteen-inch circles and the radial lines as guides. Both plates should be treated in this manner. Each sector should be carefully pressed down on the glass, so that it will stick smoothly without air-bubbles or creases. When all the sectors are in place the plates will appear like that shown in Figure 35.The Bosseswill have to be turned out at a wood-working mill or at some place where they have a turning-lathe. The bosses are four inches in diameter at the large end and one inch and one-half at the other. A groove is turned near the small end of each to accommodate a round leather belt.A hole should be made in each boss about half-way through from the small end. These holes should be bushed with a piece of brass tubing having an inside diameter of one-half inch. The tubing should go into the hole very snugly and be a "driven fit."Fig. 36.—A Side View of one of the Bosses, showing the Brass Bushing used.Fig. 36.—A Side View of one of the Bosses, showing the Brass Bushing used.The bosses should both be given a coat of shellac, and after this is dry, fastened to the glass plates on the same side to which the tinfoil sectors are attached. The best plan is to lay the disks on the paper pattern and adjust them until the outer edge coincides with the largest circle.Then apply somebichromate glueto the flat surface of one of the bosses and place the latter in the center of the plate in line with the smallest circle.Place a weight on the boss to hold it down firmly against the plate and leave it over night, or for ten or twelve hours, until thoroughly dry.The glue is prepared by placing some high-grade glue in a tin cup and covering it with cold water. Allow it to stand until the glue absorbs all the water it will and becomes soft. Then pour the water off and add enoughglacial acetic acidto cover the glue.Heat the mixture until it is reduced to a liquid, stirring it until it is perfectly smooth. Add a teaspoonful of powdered bichromate of potash to the glue.The glue must now be kept in the dark, for sunlight will "set" the glue so that it becomes insoluble.The Frame of the machine is composed of two strips twenty-five inches long, three inches wide, and an inch and one-half in thickness, and two cross-pieces of the same thickness and width fifteen inches long.Fig. 37.—The Frame.Fig. 37.—The Frame.Notches are cut at both sides of the base to admit the feet of the uprights.The Uprightsare seventeen inches long, three inches wide, and one and one-half inches thick.Fig. 38.—The Upright.Fig. 38.—The Upright.The notch at the foot is cut the same width as the thickness of the long members of the frame and is arranged so that when fitted in place, the foot of the upright will rest on the table in line with the bottom of the cross-pieces.The Driving-Wheelsare turned out of wood on a lathe. They are seven inches in diameter and seven-eighths of an inch thick. A groove should be turned in the edge to carry a small round leather belt. The wheels are mounted on a wooden axle made from a round curtain-pole. They are glued to the axle and arranged so that the grooves will fall directly underneath the pulleys turned in the bosses.Fig. 39.—The Driving-Wheels and Axle.Fig. 39.—The Driving-Wheels and Axle.The ends of the axle pass through the uprights, five inches above the bottom.The front end of the axle is fitted with a crank and a handle.Fig. 40—The Boss and Axle. For sake of clearness, the Plate is not shown.Fig. 40—The Boss and Axle. For sake of clearness, the Plate is not shown.The plates are mounted on short iron axles passing through the top of the upright into the brass bushings. One end of each of the axles is filed flat where it passes through the wood upright so that it may be firmly held by a set-screw and prevented from revolving.Fasten a small fiber washer to the center of one glass disk so that it will separate the plates and prevent them from touching when revolving.The collectors, quadrant rods, etc., are mounted on glass rods one inch in diameter. The bottoms of the rods fit in holes (H H) bored in the cross-pieces of the base, Figure 37. The upper ends are each fitted with a brass ball two inches in diameter. The balls are mounted on the rods by soldering a piece of brass tubing to the ball and slipping it over the rod. The rods should be of the proper length to bring the center of the balls on a line with the center of the plates.Fig. 41—Showing how the Ball, Comb, etc., are mounted on the Glass Rod.Fig. 41—Showing how the Ball, Comb, etc., are mounted on the Glass Rod.Make two forks as shown in Figure 42 out of brass rod, three-sixteenths of an inch in diameter and solder brass balls at the ends. The forks are eleven inches long.A number of small holes must be bored in the "prongs" and pins made by cutting ordinary dressmakers’ pins in half and soldering them in place. These pins, mounted on the forks, form the combs or collectors.Bore a horizontal hole through each of the brass rods on the top of the glass rods and pass the shanks of the forks through and solder them in place.One of the shanks may be provided with a discharge ball at the end as shown byD Bin Figure 44. The other is provided with a hard rubber handle made from a piece of rod. Bore a three-eighths hole directly in the top of each brass ball to receive the quadrant rods forming the spark-gap.Fig. 42.—A Comb or Collector.Fig. 42.—A Comb or Collector.The quadrant rods extend over the top of the plates and are three-eighths of an inch in diameter. They are loose in the tops of the balls so that they may be moved about or removed entirely.A small brass ball three-quarters of an inch in diameter should be soldered to the top of one of the quadrant rods and a similar ball two inches in diameter to the other.Fig. 43.—Showing how the Tinsel Brushes are arranged on the "Neutralizer" Rods.Fig. 43.—Showing how the Tinsel Brushes are arranged on the "Neutralizer" Rods.Two large brass balls, two inches in diameter, are fitted over the ends of the axles, which project through the uprights. Bore a one-quarter-inch hole through each ball at right angles to the axle and slip a one-quarter-inch brass rod through and solder it fast.Fig. 44.—The Complete Wimshurst Electric Machine.Fig. 44.—The Complete Wimshurst Electric Machine. B B B B,Brushes. C C,Combs. D B,Discharge Ball. I I,Glass Rods. H,Handle. Q Q,Quadrant Rods. S S S S S,Sectors. S G,Spark-Gap. P P,Driving-Wheels. For the sake of clearness, several of the sectors are not shown.The ends of the rods should be tipped with a bunch of tinsel or fine copper wires and be curved so that the brushes so formed will just touch the sectors on the disks when the latter are revolved.These are the neutralizers and are arranged in the approximate positions shown in Figure 44.The driving-wheels are connected to the bosses by means of small round leather belts. The belt at the rear of the machine is crossed in order to make the plates revolve in opposite directions.If the machine has been properly built it is now ready for operation. It may be necessary to charge the machine the first time that it is used by touching several of the sectors with the charged cover of an electrophorus. Then if the handle is turned the accumulated electricity should discharge across the spark-gap at the top of the machine in the form of bright blue sparks.Experiments with an Electric MachineMany interesting experiments can be performed with an electric machine. The number is almost unlimited. A few of the most instructive ones are described below. Others can be found in almost any text book on physics.The Leyden jarconsists of a glass jar coated with tinfoil part way up on both the outside and inside. Through the wooden stopper passes a brass rod or a heavy copper wire which connects with the inner coating of tinfoil by means of a small brass chain. The upper and outside end of the rod usually terminates in a brass ball or knob.It is a very simple matter to make a good Leyden jar.Fig. 45.—The Leyden Jar.Fig. 45.—The Leyden Jar.The jar must be thoroughly cleaned and dried before coating. The inside is then given a thorough brushing over with shellac or varnish. Before it is dry, carefully insert the tin-foil and press it smoothly against the glass. The outside of the jar is treated and coated in the same manner. The inside and outside of the bottom are also coated by cutting the tinfoil in circular pieces and shellacking them on.In order to charge the Leyden jar, grasp it in the hand near the bottom and hold the knob against the prime conductor while turning the handle of the machine.Fig. 46.—A Wooden Mortar for Igniting Gunpowder.Fig. 46.—A Wooden Mortar for Igniting Gunpowder.Igniting gunpowder.Bore a hole one-half inch in diameter and one inch deep in a block of hardwood. Pass two small brass wires through holes in the sides, letting the ends of the wires be about one-eighth of an inch apart. Pour a little gunpowder in loosely over the wires. Tie a piece of thoroughly moistened cotton twine, three inches long, to one of the wires and attach it to the outside coating of a charged Leyden jar.Connect the knob of the jar to the other wire. The gunpowder will immediately explode. Keep the face and hands away from the gunpowder when performing this experiment.Fig. 47.—An Electric Umbrella.Fig. 47.—An Electric Umbrella.Electric Umbrella.The repulsion of similarly electrified bodies which was illustrated by the action of the pith ball electroscope may be better illustrated by pasting some narrow streamers of tissue paper about one-eighth of an inch wide and four inches long to a small cork covered with tinfoil. The cork is mounted on the upper end of a stiff copper wire supported in a bottle. When the wire is connected to the prime conductor and the machine set in motion, the strips will spread out like an umbrella.Lightning Board.A pane of glass is thoroughly cleaned and then given a coat of shellac or varnish. Before the varnish is dry, press on a piece of tinfoil large enough to cover one side of the glass and rub it down smoothly.Fig. 48.—A Lightning Board.Fig. 48.—A Lightning Board.After the shellac or varnish is dry, cut the tinfoil up into innumerable little squares with a sharp knife and ruler, leaving two solid strips of tinfoil at the ends of the glass pane.The pane is mounted by cementing it in a slot in the cork of a bottle. Connect one of the tinfoil strips to the prime conductor and the other to the earth or the body. When the machine is turned, innumerable little sparks will pass between the tinfoil squares and give an appearance very similar to that of lightning.Fig. 49.—An Electric Dance.Fig. 49.—An Electric Dance.The Electrical Dance.A number of little balls of cork or pith are enclosed in a cylinder of glass about two and one-half or three inches high formed by cutting off the top of a lamp chimney. The top and bottom of the cylinder are closed by two circular pieces of sheet brass or copper. The top disk is connected to the prime conductor while the bottom one is connected to the rubber. When the machine is set in motion, the little balls will dance up and down. Bits of feather or paper cut to represent figures of men and women may be used as well as pith or cork balls.The Electric Whirl.The whirl consists of an S shaped piece of brass wire, pointed at both ends and supported on a needle by a little conical depression made in the center with a punch.Fig. 50.—An Electric Whirl.Fig. 50.—An Electric Whirl.The needle is stuck in a cork in the top of a bottle and connected with the prime conductor of the electric machine. When the latter is set in motion, the whirl will commence to revolve at a high rate of speed.Lichtenberg’s Figurescan be produced by charging a Leyden jar by connecting the knob or inside coating with the prime conductor and holding the outside coating in the hand.Then trace a small circle on the electrophorus bed with the knob.Charge a second Leyden jar by connecting the outside coating with the prime conductor.The inside coating should be connected to the rubber by means of a wire fastened to the knob. The same result may be obtained by connecting the outside coating with the prime conductor and touching the knob with the hand.Then trace a cross on the electrophorus bed with the knob, making the cross inside of the circle.Fig. 51.—Lichtenberg's Figures.Fig. 51.—Lichtenberg's Figures.Shake a mixture of red lead and sulphur through a muslin bag from a height of several inches over the electrophorus.The red lead will accumulate around the cross and the sulphur around the circle.CELLS AND BATTERIES
CHAPTER III STATIC ELECTRIC MACHINESA Cylinder Electric MachineThe electrophorus described in the last chapter is capable of furnishing sufficient electricity for many interesting experiments, but for the purpose of procuring larger supplies of electricity, a static electric machine is necessary.An electric machine is composed of two parts, one for producing the electricity by the friction of two surfaces rubbing against each other, and the other an arrangement for collecting the electricity thus formed.The earliest form of electric machine consisted of a ball of sulphur fixed upon a spindle which could be rotated by means of a crank. When the dry hands were pressed against the sulphur by a person standing on a cake of resin, which insulated him, sparks could be drawn from his body.Later a leather cushion was substituted for the hands, and a glass cylinder for the ball of sulphur, so that the frictional electric machine now consists of a cylinder or a disk of glass mounted upon a horizontal axis capable of being turned by a handle. A leather cushion, stuffed with horsehair and covered with a powdered amalgam of zinc or tin, presses against one side of the cylinder. A "prime" conductor in the shape of an elongated cylinder presents a row of fine metal spikes, like the teeth of a rake, to the opposite side. A flap of silk attached to the leather cushion passes over the cylinder and covers the upper half.Fig. 29.—Front View of a Cylinder Electric Machine.Fig. 29.—Front View of a Cylinder Electric Machine.When the handle of the machine is turned, the friction produced between the leather cushion and the glass generates a supply of positive electricity on the glass, which is collected, as the cylinder revolves, by the row of sharp points, and transferred to the prime conductor.The first thing required in the construction of an electric machine is a large glass bottle having a capacity of from two to four quarts.The insulating power of glass varies considerably. Common green glass (not white glass colored green by copper, but glass such as the telegraph insulators are made from) generally insulates the best. Some sorts of white glass, the Bohemian especially, are good insulators, but this quality will not usually be found in ordinary bottles.Fig. 30.—Method of Finding the Center of a Circle.Fig. 30.—Method of Finding the Center of a Circle.Select a smooth bottle which has no lettering embossed upon it, and stand it upon a piece of white paper. Trace on the paper a line around the circumference of the bottle so that the circle thus formed is of the same size as the bottom of the bottle. Lay a carpenter’s square on the circle so that the pointCjust touches the circumference. Draw a line fromAtoBwhere the sides of the square cut the circumference. The point in the middle of this line is the center of the circle.Place the paper on the bottom of the bottle so that the circle coincides with the circumference, and mark the center of the bottle.The bottle must now be drilled. This is accomplished with a small three-cornered file, the end of which has been broken off so as to form a ragged cutting edge. The file is set in a brace and used like an ordinary drill. During the boring process the drill must be frequently lubricated with a mixture of gum camphor and turpentine. The drilling, which will require almost an hour before the glass is pierced, if the bottle is a thick one, should be performed slowly and carefully, so as to avoid all danger of cracking the glass. The hole, when finished, should be from one-quarter to three-eighths of an inch in diameter.After the hole has been bored, fit a wooden plug into the neck of the bottle and cement it there with a mixture composed of one-half a pound of resin, five ounces of beeswax, one-quarter of an ounce of plaster of Paris, and three-quarters of an ounce of red ocher, melted together over a moderately warm stove. Dip the plug in the molten cement and force it into the neck of the bottle. When the cement dries it will be impossible to remove it.The sizes of bottles vary, so that it is quite impossible to give dimensions which must be closely followed in constructing the machine. Those in the text are approximate. The drawings have been made to scale so as to show the proportions the parts bear to each other.A heavy wooden base will be required to mount the machine on. Two uprights are mounted on the base to support the axis of the bottle. Through one of these bore a hole of the same diameter as the wooden plug fitted in the neck of the bottle. The end of the wooden plug projecting through the upright is notched and fitted with a crank so that the bottle may be revolved. The handle of the crank is an ordinary spool having one flange cut off and mounted with a screw and a washer.Fig. 31.—The "Rubber."Fig. 31.—The "Rubber."The machine is now ready for the "rubber" and "prime conductor." The rubber is a piece of wood one inch square and from six to eight inches long. A piece of undressed leather is tacked on as shown in the illustration and stuffed with horsehair. The wood is shellacked and covered with tin-foil previous to tacking on the leather. A strip of wood, two inches wide and one-half an inch thick, is fastened to the back of the rubber. The strip should be just long enough so that when the lower end rests on the base the rubber is level with the axis of the bottle. The lower end may be fastened to the base by means of a small brass hinge. Two rubber bands stretch from hooks between the rubber and the base so as to pull the former tightly against the bottle. The illustration shows a method of mounting the rubber on a foot-piece held to the base with a thumb-nut so that it may be slid back and forth and the pressure varied at will.The prime conductor is formed from a piece of curtain-pole two inches in diameter and eight inches long. The ends are rounded with a rasp and then smoothed with sandpaper. The whole surface is then shellacked and covered with a layer of tinfoil. The heads of a number of dressmaker’s pins are cut off, and the pins forced into the side of the prime conductor with a pair of pincers. They should form a row like the teeth of a rake about three-eighths of an inch apart. A hole is bored in the center of the under side of the prime conductor to receive a glass rod one-half inch in diameter. A second hole of the same size is bored in the base in such a position that when the glass rod is in place, the teeth on the prime conductor are on a level with the axis of the bottle, and their points about 3-32 of an inch away from the glass. The glass rod must be used in order to insulate the prime conductor and prevent the escape of the electricity. It is secured with some of the cement described on page 33. A piece of water-gauge glass may be used in place of a glass rod.Fig. 32.—The Prime Conductor or Collector.Fig. 32.—The Prime Conductor or Collector.A strip of oiled silk, or in its place a strip of silk which has been shellacked, eight or nine inches wide, and long enough to reach half-way around the bottle, is tacked to the rubber so that the silk covers the upper half of the cylinder and comes over to within one-quarter of an inch of the steel points.The machine is now complete, and when the handle is turned rapidly, you will be able to draw sparks from the prime conductor. The sparks will probably be very short, about one-half of an inch long. These can be increased, however, to three inches, if the glass is of the right quality, by treating the rubber with amalgam.The amalgam is formed by melting one ounce of tin and adding to it one ounce of zinc in small bits. As soon as the zinc has also melted add to the mixture two ounces of mercury which has been previously warmed. Be careful not to inhale any of the vapor during this operation. Pour the mixture into a vessel of cold water, which will reduce the metal to small grains. Pour off the water and grind the amalgam to a powder by pounding the grains with a hammer.The leather rubber should bethinlysmeared with lard and the powdered amalgam rubbed on it.In order to obtain the greatest effect from an electric machine, it must be carefully freed from dust and particles of amalgam adhering to the glass, and the insulating column rubbed with a warm woolen cloth. The best results are obtained by placing the machine near a stove or radiator where it is warm.Fig. 33.—The Complete Cylinder Electric Machine.Fig. 33.—The Complete Cylinder Electric Machine.A Wimshurst MachineThe Wimshurst Machine consists of two varnished glass plates revolving in opposite directions. On the outside of each of these plates are cemented a number of tinfoil "sectors," arranged radially. Two conductors at right angles to each other extend obliquely across the plates, one at the back and the other at the front. These conductors each terminate in brushes of tinsel which electrically excite the "sectors" as the plates revolve. The electricity is collected by a set of "collectors" arranged in a somewhat similar manner to the collector on the cylinder electric machine.The Glass Platesare each eighteen inches in diameter. Purchase two panes of clear glass twenty inches square from a glass dealer. The white glass is far preferable to the green glass and will make the best electric machine. The plates should be of the thickness known as "single light" and should be perfectly free from wavy places, bubbles, or other imperfections.Fig. 34.—Paper Pattern for laying out the Plates.Fig. 34.—Paper Pattern for laying out the Plates.The work is first laid out on a piece of stiff paper twenty inches square as a pattern. Describe a circle four inches in diameter. Using the same center, draw other circles, making them respectively eight, sixteen, and eighteen inches in diameter. Then mark sixteen radial lines, from the center, making them equal distances apart, as shown in Figure 34.Fig. 35.—Plate with Sectors in Position, and a Pattern for the Sectors.Fig. 35.—Plate with Sectors in Position, and a Pattern for the Sectors.Lay one of the glass panes over the pattern and cut out a glass circle eighteen inches in diameter, or perhaps you may be able to have a glazier do the cutting for you and so save considerable trouble and possible breakage. Two such plates should be made.The Sectors are cut from heavy flat tinfoil according to the pattern shown in Figure 35. They should be made one inch and one-half wide at the wide end and three-quarters of an inch at the other end. They are each four inches long. Thirty-two such sectors are required. The easiest way to make them is to cut out a pattern from heavy cardboard to serve as a guide.Clean and dry both of the glass plates very carefully and then give them each two thin coats of white shellac. After they have been dried, lay one of the plates on the paper pattern so that the outside of the plate will coincide with the largest circle on the paper.Then place a weight in the center of the plate so that it will not move, and stick sixteen of the tinfoil sectors on the plate with thick shellac. The sectors are arranged symmetrically on the plate, using the eight-inch and sixteen-inch circles and the radial lines as guides. Both plates should be treated in this manner. Each sector should be carefully pressed down on the glass, so that it will stick smoothly without air-bubbles or creases. When all the sectors are in place the plates will appear like that shown in Figure 35.The Bosseswill have to be turned out at a wood-working mill or at some place where they have a turning-lathe. The bosses are four inches in diameter at the large end and one inch and one-half at the other. A groove is turned near the small end of each to accommodate a round leather belt.A hole should be made in each boss about half-way through from the small end. These holes should be bushed with a piece of brass tubing having an inside diameter of one-half inch. The tubing should go into the hole very snugly and be a "driven fit."Fig. 36.—A Side View of one of the Bosses, showing the Brass Bushing used.Fig. 36.—A Side View of one of the Bosses, showing the Brass Bushing used.The bosses should both be given a coat of shellac, and after this is dry, fastened to the glass plates on the same side to which the tinfoil sectors are attached. The best plan is to lay the disks on the paper pattern and adjust them until the outer edge coincides with the largest circle.Then apply somebichromate glueto the flat surface of one of the bosses and place the latter in the center of the plate in line with the smallest circle.Place a weight on the boss to hold it down firmly against the plate and leave it over night, or for ten or twelve hours, until thoroughly dry.The glue is prepared by placing some high-grade glue in a tin cup and covering it with cold water. Allow it to stand until the glue absorbs all the water it will and becomes soft. Then pour the water off and add enoughglacial acetic acidto cover the glue.Heat the mixture until it is reduced to a liquid, stirring it until it is perfectly smooth. Add a teaspoonful of powdered bichromate of potash to the glue.The glue must now be kept in the dark, for sunlight will "set" the glue so that it becomes insoluble.The Frame of the machine is composed of two strips twenty-five inches long, three inches wide, and an inch and one-half in thickness, and two cross-pieces of the same thickness and width fifteen inches long.Fig. 37.—The Frame.Fig. 37.—The Frame.Notches are cut at both sides of the base to admit the feet of the uprights.The Uprightsare seventeen inches long, three inches wide, and one and one-half inches thick.Fig. 38.—The Upright.Fig. 38.—The Upright.The notch at the foot is cut the same width as the thickness of the long members of the frame and is arranged so that when fitted in place, the foot of the upright will rest on the table in line with the bottom of the cross-pieces.The Driving-Wheelsare turned out of wood on a lathe. They are seven inches in diameter and seven-eighths of an inch thick. A groove should be turned in the edge to carry a small round leather belt. The wheels are mounted on a wooden axle made from a round curtain-pole. They are glued to the axle and arranged so that the grooves will fall directly underneath the pulleys turned in the bosses.Fig. 39.—The Driving-Wheels and Axle.Fig. 39.—The Driving-Wheels and Axle.The ends of the axle pass through the uprights, five inches above the bottom.The front end of the axle is fitted with a crank and a handle.Fig. 40—The Boss and Axle. For sake of clearness, the Plate is not shown.Fig. 40—The Boss and Axle. For sake of clearness, the Plate is not shown.The plates are mounted on short iron axles passing through the top of the upright into the brass bushings. One end of each of the axles is filed flat where it passes through the wood upright so that it may be firmly held by a set-screw and prevented from revolving.Fasten a small fiber washer to the center of one glass disk so that it will separate the plates and prevent them from touching when revolving.The collectors, quadrant rods, etc., are mounted on glass rods one inch in diameter. The bottoms of the rods fit in holes (H H) bored in the cross-pieces of the base, Figure 37. The upper ends are each fitted with a brass ball two inches in diameter. The balls are mounted on the rods by soldering a piece of brass tubing to the ball and slipping it over the rod. The rods should be of the proper length to bring the center of the balls on a line with the center of the plates.Fig. 41—Showing how the Ball, Comb, etc., are mounted on the Glass Rod.Fig. 41—Showing how the Ball, Comb, etc., are mounted on the Glass Rod.Make two forks as shown in Figure 42 out of brass rod, three-sixteenths of an inch in diameter and solder brass balls at the ends. The forks are eleven inches long.A number of small holes must be bored in the "prongs" and pins made by cutting ordinary dressmakers’ pins in half and soldering them in place. These pins, mounted on the forks, form the combs or collectors.Bore a horizontal hole through each of the brass rods on the top of the glass rods and pass the shanks of the forks through and solder them in place.One of the shanks may be provided with a discharge ball at the end as shown byD Bin Figure 44. The other is provided with a hard rubber handle made from a piece of rod. Bore a three-eighths hole directly in the top of each brass ball to receive the quadrant rods forming the spark-gap.Fig. 42.—A Comb or Collector.Fig. 42.—A Comb or Collector.The quadrant rods extend over the top of the plates and are three-eighths of an inch in diameter. They are loose in the tops of the balls so that they may be moved about or removed entirely.A small brass ball three-quarters of an inch in diameter should be soldered to the top of one of the quadrant rods and a similar ball two inches in diameter to the other.Fig. 43.—Showing how the Tinsel Brushes are arranged on the "Neutralizer" Rods.Fig. 43.—Showing how the Tinsel Brushes are arranged on the "Neutralizer" Rods.Two large brass balls, two inches in diameter, are fitted over the ends of the axles, which project through the uprights. Bore a one-quarter-inch hole through each ball at right angles to the axle and slip a one-quarter-inch brass rod through and solder it fast.Fig. 44.—The Complete Wimshurst Electric Machine.Fig. 44.—The Complete Wimshurst Electric Machine. B B B B,Brushes. C C,Combs. D B,Discharge Ball. I I,Glass Rods. H,Handle. Q Q,Quadrant Rods. S S S S S,Sectors. S G,Spark-Gap. P P,Driving-Wheels. For the sake of clearness, several of the sectors are not shown.The ends of the rods should be tipped with a bunch of tinsel or fine copper wires and be curved so that the brushes so formed will just touch the sectors on the disks when the latter are revolved.These are the neutralizers and are arranged in the approximate positions shown in Figure 44.The driving-wheels are connected to the bosses by means of small round leather belts. The belt at the rear of the machine is crossed in order to make the plates revolve in opposite directions.If the machine has been properly built it is now ready for operation. It may be necessary to charge the machine the first time that it is used by touching several of the sectors with the charged cover of an electrophorus. Then if the handle is turned the accumulated electricity should discharge across the spark-gap at the top of the machine in the form of bright blue sparks.Experiments with an Electric MachineMany interesting experiments can be performed with an electric machine. The number is almost unlimited. A few of the most instructive ones are described below. Others can be found in almost any text book on physics.The Leyden jarconsists of a glass jar coated with tinfoil part way up on both the outside and inside. Through the wooden stopper passes a brass rod or a heavy copper wire which connects with the inner coating of tinfoil by means of a small brass chain. The upper and outside end of the rod usually terminates in a brass ball or knob.It is a very simple matter to make a good Leyden jar.Fig. 45.—The Leyden Jar.Fig. 45.—The Leyden Jar.The jar must be thoroughly cleaned and dried before coating. The inside is then given a thorough brushing over with shellac or varnish. Before it is dry, carefully insert the tin-foil and press it smoothly against the glass. The outside of the jar is treated and coated in the same manner. The inside and outside of the bottom are also coated by cutting the tinfoil in circular pieces and shellacking them on.In order to charge the Leyden jar, grasp it in the hand near the bottom and hold the knob against the prime conductor while turning the handle of the machine.Fig. 46.—A Wooden Mortar for Igniting Gunpowder.Fig. 46.—A Wooden Mortar for Igniting Gunpowder.Igniting gunpowder.Bore a hole one-half inch in diameter and one inch deep in a block of hardwood. Pass two small brass wires through holes in the sides, letting the ends of the wires be about one-eighth of an inch apart. Pour a little gunpowder in loosely over the wires. Tie a piece of thoroughly moistened cotton twine, three inches long, to one of the wires and attach it to the outside coating of a charged Leyden jar.Connect the knob of the jar to the other wire. The gunpowder will immediately explode. Keep the face and hands away from the gunpowder when performing this experiment.Fig. 47.—An Electric Umbrella.Fig. 47.—An Electric Umbrella.Electric Umbrella.The repulsion of similarly electrified bodies which was illustrated by the action of the pith ball electroscope may be better illustrated by pasting some narrow streamers of tissue paper about one-eighth of an inch wide and four inches long to a small cork covered with tinfoil. The cork is mounted on the upper end of a stiff copper wire supported in a bottle. When the wire is connected to the prime conductor and the machine set in motion, the strips will spread out like an umbrella.Lightning Board.A pane of glass is thoroughly cleaned and then given a coat of shellac or varnish. Before the varnish is dry, press on a piece of tinfoil large enough to cover one side of the glass and rub it down smoothly.Fig. 48.—A Lightning Board.Fig. 48.—A Lightning Board.After the shellac or varnish is dry, cut the tinfoil up into innumerable little squares with a sharp knife and ruler, leaving two solid strips of tinfoil at the ends of the glass pane.The pane is mounted by cementing it in a slot in the cork of a bottle. Connect one of the tinfoil strips to the prime conductor and the other to the earth or the body. When the machine is turned, innumerable little sparks will pass between the tinfoil squares and give an appearance very similar to that of lightning.Fig. 49.—An Electric Dance.Fig. 49.—An Electric Dance.The Electrical Dance.A number of little balls of cork or pith are enclosed in a cylinder of glass about two and one-half or three inches high formed by cutting off the top of a lamp chimney. The top and bottom of the cylinder are closed by two circular pieces of sheet brass or copper. The top disk is connected to the prime conductor while the bottom one is connected to the rubber. When the machine is set in motion, the little balls will dance up and down. Bits of feather or paper cut to represent figures of men and women may be used as well as pith or cork balls.The Electric Whirl.The whirl consists of an S shaped piece of brass wire, pointed at both ends and supported on a needle by a little conical depression made in the center with a punch.Fig. 50.—An Electric Whirl.Fig. 50.—An Electric Whirl.The needle is stuck in a cork in the top of a bottle and connected with the prime conductor of the electric machine. When the latter is set in motion, the whirl will commence to revolve at a high rate of speed.Lichtenberg’s Figurescan be produced by charging a Leyden jar by connecting the knob or inside coating with the prime conductor and holding the outside coating in the hand.Then trace a small circle on the electrophorus bed with the knob.Charge a second Leyden jar by connecting the outside coating with the prime conductor.The inside coating should be connected to the rubber by means of a wire fastened to the knob. The same result may be obtained by connecting the outside coating with the prime conductor and touching the knob with the hand.Then trace a cross on the electrophorus bed with the knob, making the cross inside of the circle.Fig. 51.—Lichtenberg's Figures.Fig. 51.—Lichtenberg's Figures.Shake a mixture of red lead and sulphur through a muslin bag from a height of several inches over the electrophorus.The red lead will accumulate around the cross and the sulphur around the circle.CELLS AND BATTERIES
A Cylinder Electric MachineThe electrophorus described in the last chapter is capable of furnishing sufficient electricity for many interesting experiments, but for the purpose of procuring larger supplies of electricity, a static electric machine is necessary.An electric machine is composed of two parts, one for producing the electricity by the friction of two surfaces rubbing against each other, and the other an arrangement for collecting the electricity thus formed.The earliest form of electric machine consisted of a ball of sulphur fixed upon a spindle which could be rotated by means of a crank. When the dry hands were pressed against the sulphur by a person standing on a cake of resin, which insulated him, sparks could be drawn from his body.Later a leather cushion was substituted for the hands, and a glass cylinder for the ball of sulphur, so that the frictional electric machine now consists of a cylinder or a disk of glass mounted upon a horizontal axis capable of being turned by a handle. A leather cushion, stuffed with horsehair and covered with a powdered amalgam of zinc or tin, presses against one side of the cylinder. A "prime" conductor in the shape of an elongated cylinder presents a row of fine metal spikes, like the teeth of a rake, to the opposite side. A flap of silk attached to the leather cushion passes over the cylinder and covers the upper half.Fig. 29.—Front View of a Cylinder Electric Machine.Fig. 29.—Front View of a Cylinder Electric Machine.When the handle of the machine is turned, the friction produced between the leather cushion and the glass generates a supply of positive electricity on the glass, which is collected, as the cylinder revolves, by the row of sharp points, and transferred to the prime conductor.The first thing required in the construction of an electric machine is a large glass bottle having a capacity of from two to four quarts.The insulating power of glass varies considerably. Common green glass (not white glass colored green by copper, but glass such as the telegraph insulators are made from) generally insulates the best. Some sorts of white glass, the Bohemian especially, are good insulators, but this quality will not usually be found in ordinary bottles.Fig. 30.—Method of Finding the Center of a Circle.Fig. 30.—Method of Finding the Center of a Circle.Select a smooth bottle which has no lettering embossed upon it, and stand it upon a piece of white paper. Trace on the paper a line around the circumference of the bottle so that the circle thus formed is of the same size as the bottom of the bottle. Lay a carpenter’s square on the circle so that the pointCjust touches the circumference. Draw a line fromAtoBwhere the sides of the square cut the circumference. The point in the middle of this line is the center of the circle.Place the paper on the bottom of the bottle so that the circle coincides with the circumference, and mark the center of the bottle.The bottle must now be drilled. This is accomplished with a small three-cornered file, the end of which has been broken off so as to form a ragged cutting edge. The file is set in a brace and used like an ordinary drill. During the boring process the drill must be frequently lubricated with a mixture of gum camphor and turpentine. The drilling, which will require almost an hour before the glass is pierced, if the bottle is a thick one, should be performed slowly and carefully, so as to avoid all danger of cracking the glass. The hole, when finished, should be from one-quarter to three-eighths of an inch in diameter.After the hole has been bored, fit a wooden plug into the neck of the bottle and cement it there with a mixture composed of one-half a pound of resin, five ounces of beeswax, one-quarter of an ounce of plaster of Paris, and three-quarters of an ounce of red ocher, melted together over a moderately warm stove. Dip the plug in the molten cement and force it into the neck of the bottle. When the cement dries it will be impossible to remove it.The sizes of bottles vary, so that it is quite impossible to give dimensions which must be closely followed in constructing the machine. Those in the text are approximate. The drawings have been made to scale so as to show the proportions the parts bear to each other.A heavy wooden base will be required to mount the machine on. Two uprights are mounted on the base to support the axis of the bottle. Through one of these bore a hole of the same diameter as the wooden plug fitted in the neck of the bottle. The end of the wooden plug projecting through the upright is notched and fitted with a crank so that the bottle may be revolved. The handle of the crank is an ordinary spool having one flange cut off and mounted with a screw and a washer.Fig. 31.—The "Rubber."Fig. 31.—The "Rubber."The machine is now ready for the "rubber" and "prime conductor." The rubber is a piece of wood one inch square and from six to eight inches long. A piece of undressed leather is tacked on as shown in the illustration and stuffed with horsehair. The wood is shellacked and covered with tin-foil previous to tacking on the leather. A strip of wood, two inches wide and one-half an inch thick, is fastened to the back of the rubber. The strip should be just long enough so that when the lower end rests on the base the rubber is level with the axis of the bottle. The lower end may be fastened to the base by means of a small brass hinge. Two rubber bands stretch from hooks between the rubber and the base so as to pull the former tightly against the bottle. The illustration shows a method of mounting the rubber on a foot-piece held to the base with a thumb-nut so that it may be slid back and forth and the pressure varied at will.The prime conductor is formed from a piece of curtain-pole two inches in diameter and eight inches long. The ends are rounded with a rasp and then smoothed with sandpaper. The whole surface is then shellacked and covered with a layer of tinfoil. The heads of a number of dressmaker’s pins are cut off, and the pins forced into the side of the prime conductor with a pair of pincers. They should form a row like the teeth of a rake about three-eighths of an inch apart. A hole is bored in the center of the under side of the prime conductor to receive a glass rod one-half inch in diameter. A second hole of the same size is bored in the base in such a position that when the glass rod is in place, the teeth on the prime conductor are on a level with the axis of the bottle, and their points about 3-32 of an inch away from the glass. The glass rod must be used in order to insulate the prime conductor and prevent the escape of the electricity. It is secured with some of the cement described on page 33. A piece of water-gauge glass may be used in place of a glass rod.Fig. 32.—The Prime Conductor or Collector.Fig. 32.—The Prime Conductor or Collector.A strip of oiled silk, or in its place a strip of silk which has been shellacked, eight or nine inches wide, and long enough to reach half-way around the bottle, is tacked to the rubber so that the silk covers the upper half of the cylinder and comes over to within one-quarter of an inch of the steel points.The machine is now complete, and when the handle is turned rapidly, you will be able to draw sparks from the prime conductor. The sparks will probably be very short, about one-half of an inch long. These can be increased, however, to three inches, if the glass is of the right quality, by treating the rubber with amalgam.The amalgam is formed by melting one ounce of tin and adding to it one ounce of zinc in small bits. As soon as the zinc has also melted add to the mixture two ounces of mercury which has been previously warmed. Be careful not to inhale any of the vapor during this operation. Pour the mixture into a vessel of cold water, which will reduce the metal to small grains. Pour off the water and grind the amalgam to a powder by pounding the grains with a hammer.The leather rubber should bethinlysmeared with lard and the powdered amalgam rubbed on it.In order to obtain the greatest effect from an electric machine, it must be carefully freed from dust and particles of amalgam adhering to the glass, and the insulating column rubbed with a warm woolen cloth. The best results are obtained by placing the machine near a stove or radiator where it is warm.Fig. 33.—The Complete Cylinder Electric Machine.Fig. 33.—The Complete Cylinder Electric Machine.
The electrophorus described in the last chapter is capable of furnishing sufficient electricity for many interesting experiments, but for the purpose of procuring larger supplies of electricity, a static electric machine is necessary.
An electric machine is composed of two parts, one for producing the electricity by the friction of two surfaces rubbing against each other, and the other an arrangement for collecting the electricity thus formed.
The earliest form of electric machine consisted of a ball of sulphur fixed upon a spindle which could be rotated by means of a crank. When the dry hands were pressed against the sulphur by a person standing on a cake of resin, which insulated him, sparks could be drawn from his body.
Later a leather cushion was substituted for the hands, and a glass cylinder for the ball of sulphur, so that the frictional electric machine now consists of a cylinder or a disk of glass mounted upon a horizontal axis capable of being turned by a handle. A leather cushion, stuffed with horsehair and covered with a powdered amalgam of zinc or tin, presses against one side of the cylinder. A "prime" conductor in the shape of an elongated cylinder presents a row of fine metal spikes, like the teeth of a rake, to the opposite side. A flap of silk attached to the leather cushion passes over the cylinder and covers the upper half.
Fig. 29.—Front View of a Cylinder Electric Machine.Fig. 29.—Front View of a Cylinder Electric Machine.
Fig. 29.—Front View of a Cylinder Electric Machine.
When the handle of the machine is turned, the friction produced between the leather cushion and the glass generates a supply of positive electricity on the glass, which is collected, as the cylinder revolves, by the row of sharp points, and transferred to the prime conductor.
The first thing required in the construction of an electric machine is a large glass bottle having a capacity of from two to four quarts.
The insulating power of glass varies considerably. Common green glass (not white glass colored green by copper, but glass such as the telegraph insulators are made from) generally insulates the best. Some sorts of white glass, the Bohemian especially, are good insulators, but this quality will not usually be found in ordinary bottles.
Fig. 30.—Method of Finding the Center of a Circle.Fig. 30.—Method of Finding the Center of a Circle.
Fig. 30.—Method of Finding the Center of a Circle.
Select a smooth bottle which has no lettering embossed upon it, and stand it upon a piece of white paper. Trace on the paper a line around the circumference of the bottle so that the circle thus formed is of the same size as the bottom of the bottle. Lay a carpenter’s square on the circle so that the pointCjust touches the circumference. Draw a line fromAtoBwhere the sides of the square cut the circumference. The point in the middle of this line is the center of the circle.
Place the paper on the bottom of the bottle so that the circle coincides with the circumference, and mark the center of the bottle.
The bottle must now be drilled. This is accomplished with a small three-cornered file, the end of which has been broken off so as to form a ragged cutting edge. The file is set in a brace and used like an ordinary drill. During the boring process the drill must be frequently lubricated with a mixture of gum camphor and turpentine. The drilling, which will require almost an hour before the glass is pierced, if the bottle is a thick one, should be performed slowly and carefully, so as to avoid all danger of cracking the glass. The hole, when finished, should be from one-quarter to three-eighths of an inch in diameter.
After the hole has been bored, fit a wooden plug into the neck of the bottle and cement it there with a mixture composed of one-half a pound of resin, five ounces of beeswax, one-quarter of an ounce of plaster of Paris, and three-quarters of an ounce of red ocher, melted together over a moderately warm stove. Dip the plug in the molten cement and force it into the neck of the bottle. When the cement dries it will be impossible to remove it.
The sizes of bottles vary, so that it is quite impossible to give dimensions which must be closely followed in constructing the machine. Those in the text are approximate. The drawings have been made to scale so as to show the proportions the parts bear to each other.
A heavy wooden base will be required to mount the machine on. Two uprights are mounted on the base to support the axis of the bottle. Through one of these bore a hole of the same diameter as the wooden plug fitted in the neck of the bottle. The end of the wooden plug projecting through the upright is notched and fitted with a crank so that the bottle may be revolved. The handle of the crank is an ordinary spool having one flange cut off and mounted with a screw and a washer.
Fig. 31.—The "Rubber."Fig. 31.—The "Rubber."
Fig. 31.—The "Rubber."
The machine is now ready for the "rubber" and "prime conductor." The rubber is a piece of wood one inch square and from six to eight inches long. A piece of undressed leather is tacked on as shown in the illustration and stuffed with horsehair. The wood is shellacked and covered with tin-foil previous to tacking on the leather. A strip of wood, two inches wide and one-half an inch thick, is fastened to the back of the rubber. The strip should be just long enough so that when the lower end rests on the base the rubber is level with the axis of the bottle. The lower end may be fastened to the base by means of a small brass hinge. Two rubber bands stretch from hooks between the rubber and the base so as to pull the former tightly against the bottle. The illustration shows a method of mounting the rubber on a foot-piece held to the base with a thumb-nut so that it may be slid back and forth and the pressure varied at will.
The prime conductor is formed from a piece of curtain-pole two inches in diameter and eight inches long. The ends are rounded with a rasp and then smoothed with sandpaper. The whole surface is then shellacked and covered with a layer of tinfoil. The heads of a number of dressmaker’s pins are cut off, and the pins forced into the side of the prime conductor with a pair of pincers. They should form a row like the teeth of a rake about three-eighths of an inch apart. A hole is bored in the center of the under side of the prime conductor to receive a glass rod one-half inch in diameter. A second hole of the same size is bored in the base in such a position that when the glass rod is in place, the teeth on the prime conductor are on a level with the axis of the bottle, and their points about 3-32 of an inch away from the glass. The glass rod must be used in order to insulate the prime conductor and prevent the escape of the electricity. It is secured with some of the cement described on page 33. A piece of water-gauge glass may be used in place of a glass rod.
Fig. 32.—The Prime Conductor or Collector.Fig. 32.—The Prime Conductor or Collector.
Fig. 32.—The Prime Conductor or Collector.
A strip of oiled silk, or in its place a strip of silk which has been shellacked, eight or nine inches wide, and long enough to reach half-way around the bottle, is tacked to the rubber so that the silk covers the upper half of the cylinder and comes over to within one-quarter of an inch of the steel points.
The machine is now complete, and when the handle is turned rapidly, you will be able to draw sparks from the prime conductor. The sparks will probably be very short, about one-half of an inch long. These can be increased, however, to three inches, if the glass is of the right quality, by treating the rubber with amalgam.
The amalgam is formed by melting one ounce of tin and adding to it one ounce of zinc in small bits. As soon as the zinc has also melted add to the mixture two ounces of mercury which has been previously warmed. Be careful not to inhale any of the vapor during this operation. Pour the mixture into a vessel of cold water, which will reduce the metal to small grains. Pour off the water and grind the amalgam to a powder by pounding the grains with a hammer.
The leather rubber should bethinlysmeared with lard and the powdered amalgam rubbed on it.
In order to obtain the greatest effect from an electric machine, it must be carefully freed from dust and particles of amalgam adhering to the glass, and the insulating column rubbed with a warm woolen cloth. The best results are obtained by placing the machine near a stove or radiator where it is warm.
Fig. 33.—The Complete Cylinder Electric Machine.Fig. 33.—The Complete Cylinder Electric Machine.
Fig. 33.—The Complete Cylinder Electric Machine.
A Wimshurst MachineThe Wimshurst Machine consists of two varnished glass plates revolving in opposite directions. On the outside of each of these plates are cemented a number of tinfoil "sectors," arranged radially. Two conductors at right angles to each other extend obliquely across the plates, one at the back and the other at the front. These conductors each terminate in brushes of tinsel which electrically excite the "sectors" as the plates revolve. The electricity is collected by a set of "collectors" arranged in a somewhat similar manner to the collector on the cylinder electric machine.The Glass Platesare each eighteen inches in diameter. Purchase two panes of clear glass twenty inches square from a glass dealer. The white glass is far preferable to the green glass and will make the best electric machine. The plates should be of the thickness known as "single light" and should be perfectly free from wavy places, bubbles, or other imperfections.Fig. 34.—Paper Pattern for laying out the Plates.Fig. 34.—Paper Pattern for laying out the Plates.The work is first laid out on a piece of stiff paper twenty inches square as a pattern. Describe a circle four inches in diameter. Using the same center, draw other circles, making them respectively eight, sixteen, and eighteen inches in diameter. Then mark sixteen radial lines, from the center, making them equal distances apart, as shown in Figure 34.Fig. 35.—Plate with Sectors in Position, and a Pattern for the Sectors.Fig. 35.—Plate with Sectors in Position, and a Pattern for the Sectors.Lay one of the glass panes over the pattern and cut out a glass circle eighteen inches in diameter, or perhaps you may be able to have a glazier do the cutting for you and so save considerable trouble and possible breakage. Two such plates should be made.The Sectors are cut from heavy flat tinfoil according to the pattern shown in Figure 35. They should be made one inch and one-half wide at the wide end and three-quarters of an inch at the other end. They are each four inches long. Thirty-two such sectors are required. The easiest way to make them is to cut out a pattern from heavy cardboard to serve as a guide.Clean and dry both of the glass plates very carefully and then give them each two thin coats of white shellac. After they have been dried, lay one of the plates on the paper pattern so that the outside of the plate will coincide with the largest circle on the paper.Then place a weight in the center of the plate so that it will not move, and stick sixteen of the tinfoil sectors on the plate with thick shellac. The sectors are arranged symmetrically on the plate, using the eight-inch and sixteen-inch circles and the radial lines as guides. Both plates should be treated in this manner. Each sector should be carefully pressed down on the glass, so that it will stick smoothly without air-bubbles or creases. When all the sectors are in place the plates will appear like that shown in Figure 35.The Bosseswill have to be turned out at a wood-working mill or at some place where they have a turning-lathe. The bosses are four inches in diameter at the large end and one inch and one-half at the other. A groove is turned near the small end of each to accommodate a round leather belt.A hole should be made in each boss about half-way through from the small end. These holes should be bushed with a piece of brass tubing having an inside diameter of one-half inch. The tubing should go into the hole very snugly and be a "driven fit."Fig. 36.—A Side View of one of the Bosses, showing the Brass Bushing used.Fig. 36.—A Side View of one of the Bosses, showing the Brass Bushing used.The bosses should both be given a coat of shellac, and after this is dry, fastened to the glass plates on the same side to which the tinfoil sectors are attached. The best plan is to lay the disks on the paper pattern and adjust them until the outer edge coincides with the largest circle.Then apply somebichromate glueto the flat surface of one of the bosses and place the latter in the center of the plate in line with the smallest circle.Place a weight on the boss to hold it down firmly against the plate and leave it over night, or for ten or twelve hours, until thoroughly dry.The glue is prepared by placing some high-grade glue in a tin cup and covering it with cold water. Allow it to stand until the glue absorbs all the water it will and becomes soft. Then pour the water off and add enoughglacial acetic acidto cover the glue.Heat the mixture until it is reduced to a liquid, stirring it until it is perfectly smooth. Add a teaspoonful of powdered bichromate of potash to the glue.The glue must now be kept in the dark, for sunlight will "set" the glue so that it becomes insoluble.The Frame of the machine is composed of two strips twenty-five inches long, three inches wide, and an inch and one-half in thickness, and two cross-pieces of the same thickness and width fifteen inches long.Fig. 37.—The Frame.Fig. 37.—The Frame.Notches are cut at both sides of the base to admit the feet of the uprights.The Uprightsare seventeen inches long, three inches wide, and one and one-half inches thick.Fig. 38.—The Upright.Fig. 38.—The Upright.The notch at the foot is cut the same width as the thickness of the long members of the frame and is arranged so that when fitted in place, the foot of the upright will rest on the table in line with the bottom of the cross-pieces.The Driving-Wheelsare turned out of wood on a lathe. They are seven inches in diameter and seven-eighths of an inch thick. A groove should be turned in the edge to carry a small round leather belt. The wheels are mounted on a wooden axle made from a round curtain-pole. They are glued to the axle and arranged so that the grooves will fall directly underneath the pulleys turned in the bosses.Fig. 39.—The Driving-Wheels and Axle.Fig. 39.—The Driving-Wheels and Axle.The ends of the axle pass through the uprights, five inches above the bottom.The front end of the axle is fitted with a crank and a handle.Fig. 40—The Boss and Axle. For sake of clearness, the Plate is not shown.Fig. 40—The Boss and Axle. For sake of clearness, the Plate is not shown.The plates are mounted on short iron axles passing through the top of the upright into the brass bushings. One end of each of the axles is filed flat where it passes through the wood upright so that it may be firmly held by a set-screw and prevented from revolving.Fasten a small fiber washer to the center of one glass disk so that it will separate the plates and prevent them from touching when revolving.The collectors, quadrant rods, etc., are mounted on glass rods one inch in diameter. The bottoms of the rods fit in holes (H H) bored in the cross-pieces of the base, Figure 37. The upper ends are each fitted with a brass ball two inches in diameter. The balls are mounted on the rods by soldering a piece of brass tubing to the ball and slipping it over the rod. The rods should be of the proper length to bring the center of the balls on a line with the center of the plates.Fig. 41—Showing how the Ball, Comb, etc., are mounted on the Glass Rod.Fig. 41—Showing how the Ball, Comb, etc., are mounted on the Glass Rod.Make two forks as shown in Figure 42 out of brass rod, three-sixteenths of an inch in diameter and solder brass balls at the ends. The forks are eleven inches long.A number of small holes must be bored in the "prongs" and pins made by cutting ordinary dressmakers’ pins in half and soldering them in place. These pins, mounted on the forks, form the combs or collectors.Bore a horizontal hole through each of the brass rods on the top of the glass rods and pass the shanks of the forks through and solder them in place.One of the shanks may be provided with a discharge ball at the end as shown byD Bin Figure 44. The other is provided with a hard rubber handle made from a piece of rod. Bore a three-eighths hole directly in the top of each brass ball to receive the quadrant rods forming the spark-gap.Fig. 42.—A Comb or Collector.Fig. 42.—A Comb or Collector.The quadrant rods extend over the top of the plates and are three-eighths of an inch in diameter. They are loose in the tops of the balls so that they may be moved about or removed entirely.A small brass ball three-quarters of an inch in diameter should be soldered to the top of one of the quadrant rods and a similar ball two inches in diameter to the other.Fig. 43.—Showing how the Tinsel Brushes are arranged on the "Neutralizer" Rods.Fig. 43.—Showing how the Tinsel Brushes are arranged on the "Neutralizer" Rods.Two large brass balls, two inches in diameter, are fitted over the ends of the axles, which project through the uprights. Bore a one-quarter-inch hole through each ball at right angles to the axle and slip a one-quarter-inch brass rod through and solder it fast.Fig. 44.—The Complete Wimshurst Electric Machine.Fig. 44.—The Complete Wimshurst Electric Machine. B B B B,Brushes. C C,Combs. D B,Discharge Ball. I I,Glass Rods. H,Handle. Q Q,Quadrant Rods. S S S S S,Sectors. S G,Spark-Gap. P P,Driving-Wheels. For the sake of clearness, several of the sectors are not shown.The ends of the rods should be tipped with a bunch of tinsel or fine copper wires and be curved so that the brushes so formed will just touch the sectors on the disks when the latter are revolved.These are the neutralizers and are arranged in the approximate positions shown in Figure 44.The driving-wheels are connected to the bosses by means of small round leather belts. The belt at the rear of the machine is crossed in order to make the plates revolve in opposite directions.If the machine has been properly built it is now ready for operation. It may be necessary to charge the machine the first time that it is used by touching several of the sectors with the charged cover of an electrophorus. Then if the handle is turned the accumulated electricity should discharge across the spark-gap at the top of the machine in the form of bright blue sparks.
The Wimshurst Machine consists of two varnished glass plates revolving in opposite directions. On the outside of each of these plates are cemented a number of tinfoil "sectors," arranged radially. Two conductors at right angles to each other extend obliquely across the plates, one at the back and the other at the front. These conductors each terminate in brushes of tinsel which electrically excite the "sectors" as the plates revolve. The electricity is collected by a set of "collectors" arranged in a somewhat similar manner to the collector on the cylinder electric machine.
The Glass Platesare each eighteen inches in diameter. Purchase two panes of clear glass twenty inches square from a glass dealer. The white glass is far preferable to the green glass and will make the best electric machine. The plates should be of the thickness known as "single light" and should be perfectly free from wavy places, bubbles, or other imperfections.
Fig. 34.—Paper Pattern for laying out the Plates.Fig. 34.—Paper Pattern for laying out the Plates.
Fig. 34.—Paper Pattern for laying out the Plates.
The work is first laid out on a piece of stiff paper twenty inches square as a pattern. Describe a circle four inches in diameter. Using the same center, draw other circles, making them respectively eight, sixteen, and eighteen inches in diameter. Then mark sixteen radial lines, from the center, making them equal distances apart, as shown in Figure 34.
Fig. 35.—Plate with Sectors in Position, and a Pattern for the Sectors.Fig. 35.—Plate with Sectors in Position, and a Pattern for the Sectors.
Fig. 35.—Plate with Sectors in Position, and a Pattern for the Sectors.
Lay one of the glass panes over the pattern and cut out a glass circle eighteen inches in diameter, or perhaps you may be able to have a glazier do the cutting for you and so save considerable trouble and possible breakage. Two such plates should be made.
The Sectors are cut from heavy flat tinfoil according to the pattern shown in Figure 35. They should be made one inch and one-half wide at the wide end and three-quarters of an inch at the other end. They are each four inches long. Thirty-two such sectors are required. The easiest way to make them is to cut out a pattern from heavy cardboard to serve as a guide.
Clean and dry both of the glass plates very carefully and then give them each two thin coats of white shellac. After they have been dried, lay one of the plates on the paper pattern so that the outside of the plate will coincide with the largest circle on the paper.
Then place a weight in the center of the plate so that it will not move, and stick sixteen of the tinfoil sectors on the plate with thick shellac. The sectors are arranged symmetrically on the plate, using the eight-inch and sixteen-inch circles and the radial lines as guides. Both plates should be treated in this manner. Each sector should be carefully pressed down on the glass, so that it will stick smoothly without air-bubbles or creases. When all the sectors are in place the plates will appear like that shown in Figure 35.
The Bosseswill have to be turned out at a wood-working mill or at some place where they have a turning-lathe. The bosses are four inches in diameter at the large end and one inch and one-half at the other. A groove is turned near the small end of each to accommodate a round leather belt.
A hole should be made in each boss about half-way through from the small end. These holes should be bushed with a piece of brass tubing having an inside diameter of one-half inch. The tubing should go into the hole very snugly and be a "driven fit."
Fig. 36.—A Side View of one of the Bosses, showing the Brass Bushing used.Fig. 36.—A Side View of one of the Bosses, showing the Brass Bushing used.
Fig. 36.—A Side View of one of the Bosses, showing the Brass Bushing used.
The bosses should both be given a coat of shellac, and after this is dry, fastened to the glass plates on the same side to which the tinfoil sectors are attached. The best plan is to lay the disks on the paper pattern and adjust them until the outer edge coincides with the largest circle.
Then apply somebichromate glueto the flat surface of one of the bosses and place the latter in the center of the plate in line with the smallest circle.
Place a weight on the boss to hold it down firmly against the plate and leave it over night, or for ten or twelve hours, until thoroughly dry.
The glue is prepared by placing some high-grade glue in a tin cup and covering it with cold water. Allow it to stand until the glue absorbs all the water it will and becomes soft. Then pour the water off and add enoughglacial acetic acidto cover the glue.
Heat the mixture until it is reduced to a liquid, stirring it until it is perfectly smooth. Add a teaspoonful of powdered bichromate of potash to the glue.
The glue must now be kept in the dark, for sunlight will "set" the glue so that it becomes insoluble.
The Frame of the machine is composed of two strips twenty-five inches long, three inches wide, and an inch and one-half in thickness, and two cross-pieces of the same thickness and width fifteen inches long.
Fig. 37.—The Frame.Fig. 37.—The Frame.
Fig. 37.—The Frame.
Notches are cut at both sides of the base to admit the feet of the uprights.
The Uprightsare seventeen inches long, three inches wide, and one and one-half inches thick.
Fig. 38.—The Upright.Fig. 38.—The Upright.
Fig. 38.—The Upright.
The notch at the foot is cut the same width as the thickness of the long members of the frame and is arranged so that when fitted in place, the foot of the upright will rest on the table in line with the bottom of the cross-pieces.
The Driving-Wheelsare turned out of wood on a lathe. They are seven inches in diameter and seven-eighths of an inch thick. A groove should be turned in the edge to carry a small round leather belt. The wheels are mounted on a wooden axle made from a round curtain-pole. They are glued to the axle and arranged so that the grooves will fall directly underneath the pulleys turned in the bosses.
Fig. 39.—The Driving-Wheels and Axle.Fig. 39.—The Driving-Wheels and Axle.
Fig. 39.—The Driving-Wheels and Axle.
The ends of the axle pass through the uprights, five inches above the bottom.
The front end of the axle is fitted with a crank and a handle.
Fig. 40—The Boss and Axle. For sake of clearness, the Plate is not shown.Fig. 40—The Boss and Axle. For sake of clearness, the Plate is not shown.
Fig. 40—The Boss and Axle. For sake of clearness, the Plate is not shown.
The plates are mounted on short iron axles passing through the top of the upright into the brass bushings. One end of each of the axles is filed flat where it passes through the wood upright so that it may be firmly held by a set-screw and prevented from revolving.
Fasten a small fiber washer to the center of one glass disk so that it will separate the plates and prevent them from touching when revolving.
The collectors, quadrant rods, etc., are mounted on glass rods one inch in diameter. The bottoms of the rods fit in holes (H H) bored in the cross-pieces of the base, Figure 37. The upper ends are each fitted with a brass ball two inches in diameter. The balls are mounted on the rods by soldering a piece of brass tubing to the ball and slipping it over the rod. The rods should be of the proper length to bring the center of the balls on a line with the center of the plates.
Fig. 41—Showing how the Ball, Comb, etc., are mounted on the Glass Rod.Fig. 41—Showing how the Ball, Comb, etc., are mounted on the Glass Rod.
Fig. 41—Showing how the Ball, Comb, etc., are mounted on the Glass Rod.
Make two forks as shown in Figure 42 out of brass rod, three-sixteenths of an inch in diameter and solder brass balls at the ends. The forks are eleven inches long.
A number of small holes must be bored in the "prongs" and pins made by cutting ordinary dressmakers’ pins in half and soldering them in place. These pins, mounted on the forks, form the combs or collectors.
Bore a horizontal hole through each of the brass rods on the top of the glass rods and pass the shanks of the forks through and solder them in place.
One of the shanks may be provided with a discharge ball at the end as shown byD Bin Figure 44. The other is provided with a hard rubber handle made from a piece of rod. Bore a three-eighths hole directly in the top of each brass ball to receive the quadrant rods forming the spark-gap.
Fig. 42.—A Comb or Collector.Fig. 42.—A Comb or Collector.
Fig. 42.—A Comb or Collector.
The quadrant rods extend over the top of the plates and are three-eighths of an inch in diameter. They are loose in the tops of the balls so that they may be moved about or removed entirely.
A small brass ball three-quarters of an inch in diameter should be soldered to the top of one of the quadrant rods and a similar ball two inches in diameter to the other.
Fig. 43.—Showing how the Tinsel Brushes are arranged on the "Neutralizer" Rods.Fig. 43.—Showing how the Tinsel Brushes are arranged on the "Neutralizer" Rods.
Fig. 43.—Showing how the Tinsel Brushes are arranged on the "Neutralizer" Rods.
Two large brass balls, two inches in diameter, are fitted over the ends of the axles, which project through the uprights. Bore a one-quarter-inch hole through each ball at right angles to the axle and slip a one-quarter-inch brass rod through and solder it fast.
Fig. 44.—The Complete Wimshurst Electric Machine.Fig. 44.—The Complete Wimshurst Electric Machine. B B B B,Brushes. C C,Combs. D B,Discharge Ball. I I,Glass Rods. H,Handle. Q Q,Quadrant Rods. S S S S S,Sectors. S G,Spark-Gap. P P,Driving-Wheels. For the sake of clearness, several of the sectors are not shown.
Fig. 44.—The Complete Wimshurst Electric Machine. B B B B,Brushes. C C,Combs. D B,Discharge Ball. I I,Glass Rods. H,Handle. Q Q,Quadrant Rods. S S S S S,Sectors. S G,Spark-Gap. P P,Driving-Wheels. For the sake of clearness, several of the sectors are not shown.
The ends of the rods should be tipped with a bunch of tinsel or fine copper wires and be curved so that the brushes so formed will just touch the sectors on the disks when the latter are revolved.
These are the neutralizers and are arranged in the approximate positions shown in Figure 44.
The driving-wheels are connected to the bosses by means of small round leather belts. The belt at the rear of the machine is crossed in order to make the plates revolve in opposite directions.
If the machine has been properly built it is now ready for operation. It may be necessary to charge the machine the first time that it is used by touching several of the sectors with the charged cover of an electrophorus. Then if the handle is turned the accumulated electricity should discharge across the spark-gap at the top of the machine in the form of bright blue sparks.
Experiments with an Electric MachineMany interesting experiments can be performed with an electric machine. The number is almost unlimited. A few of the most instructive ones are described below. Others can be found in almost any text book on physics.The Leyden jarconsists of a glass jar coated with tinfoil part way up on both the outside and inside. Through the wooden stopper passes a brass rod or a heavy copper wire which connects with the inner coating of tinfoil by means of a small brass chain. The upper and outside end of the rod usually terminates in a brass ball or knob.It is a very simple matter to make a good Leyden jar.Fig. 45.—The Leyden Jar.Fig. 45.—The Leyden Jar.The jar must be thoroughly cleaned and dried before coating. The inside is then given a thorough brushing over with shellac or varnish. Before it is dry, carefully insert the tin-foil and press it smoothly against the glass. The outside of the jar is treated and coated in the same manner. The inside and outside of the bottom are also coated by cutting the tinfoil in circular pieces and shellacking them on.In order to charge the Leyden jar, grasp it in the hand near the bottom and hold the knob against the prime conductor while turning the handle of the machine.Fig. 46.—A Wooden Mortar for Igniting Gunpowder.Fig. 46.—A Wooden Mortar for Igniting Gunpowder.Igniting gunpowder.Bore a hole one-half inch in diameter and one inch deep in a block of hardwood. Pass two small brass wires through holes in the sides, letting the ends of the wires be about one-eighth of an inch apart. Pour a little gunpowder in loosely over the wires. Tie a piece of thoroughly moistened cotton twine, three inches long, to one of the wires and attach it to the outside coating of a charged Leyden jar.Connect the knob of the jar to the other wire. The gunpowder will immediately explode. Keep the face and hands away from the gunpowder when performing this experiment.Fig. 47.—An Electric Umbrella.Fig. 47.—An Electric Umbrella.Electric Umbrella.The repulsion of similarly electrified bodies which was illustrated by the action of the pith ball electroscope may be better illustrated by pasting some narrow streamers of tissue paper about one-eighth of an inch wide and four inches long to a small cork covered with tinfoil. The cork is mounted on the upper end of a stiff copper wire supported in a bottle. When the wire is connected to the prime conductor and the machine set in motion, the strips will spread out like an umbrella.Lightning Board.A pane of glass is thoroughly cleaned and then given a coat of shellac or varnish. Before the varnish is dry, press on a piece of tinfoil large enough to cover one side of the glass and rub it down smoothly.Fig. 48.—A Lightning Board.Fig. 48.—A Lightning Board.After the shellac or varnish is dry, cut the tinfoil up into innumerable little squares with a sharp knife and ruler, leaving two solid strips of tinfoil at the ends of the glass pane.The pane is mounted by cementing it in a slot in the cork of a bottle. Connect one of the tinfoil strips to the prime conductor and the other to the earth or the body. When the machine is turned, innumerable little sparks will pass between the tinfoil squares and give an appearance very similar to that of lightning.Fig. 49.—An Electric Dance.Fig. 49.—An Electric Dance.The Electrical Dance.A number of little balls of cork or pith are enclosed in a cylinder of glass about two and one-half or three inches high formed by cutting off the top of a lamp chimney. The top and bottom of the cylinder are closed by two circular pieces of sheet brass or copper. The top disk is connected to the prime conductor while the bottom one is connected to the rubber. When the machine is set in motion, the little balls will dance up and down. Bits of feather or paper cut to represent figures of men and women may be used as well as pith or cork balls.The Electric Whirl.The whirl consists of an S shaped piece of brass wire, pointed at both ends and supported on a needle by a little conical depression made in the center with a punch.Fig. 50.—An Electric Whirl.Fig. 50.—An Electric Whirl.The needle is stuck in a cork in the top of a bottle and connected with the prime conductor of the electric machine. When the latter is set in motion, the whirl will commence to revolve at a high rate of speed.Lichtenberg’s Figurescan be produced by charging a Leyden jar by connecting the knob or inside coating with the prime conductor and holding the outside coating in the hand.Then trace a small circle on the electrophorus bed with the knob.Charge a second Leyden jar by connecting the outside coating with the prime conductor.The inside coating should be connected to the rubber by means of a wire fastened to the knob. The same result may be obtained by connecting the outside coating with the prime conductor and touching the knob with the hand.Then trace a cross on the electrophorus bed with the knob, making the cross inside of the circle.Fig. 51.—Lichtenberg's Figures.Fig. 51.—Lichtenberg's Figures.Shake a mixture of red lead and sulphur through a muslin bag from a height of several inches over the electrophorus.The red lead will accumulate around the cross and the sulphur around the circle.CELLS AND BATTERIES
Many interesting experiments can be performed with an electric machine. The number is almost unlimited. A few of the most instructive ones are described below. Others can be found in almost any text book on physics.
The Leyden jarconsists of a glass jar coated with tinfoil part way up on both the outside and inside. Through the wooden stopper passes a brass rod or a heavy copper wire which connects with the inner coating of tinfoil by means of a small brass chain. The upper and outside end of the rod usually terminates in a brass ball or knob.
It is a very simple matter to make a good Leyden jar.
Fig. 45.—The Leyden Jar.Fig. 45.—The Leyden Jar.
Fig. 45.—The Leyden Jar.
The jar must be thoroughly cleaned and dried before coating. The inside is then given a thorough brushing over with shellac or varnish. Before it is dry, carefully insert the tin-foil and press it smoothly against the glass. The outside of the jar is treated and coated in the same manner. The inside and outside of the bottom are also coated by cutting the tinfoil in circular pieces and shellacking them on.
In order to charge the Leyden jar, grasp it in the hand near the bottom and hold the knob against the prime conductor while turning the handle of the machine.
Fig. 46.—A Wooden Mortar for Igniting Gunpowder.Fig. 46.—A Wooden Mortar for Igniting Gunpowder.
Fig. 46.—A Wooden Mortar for Igniting Gunpowder.
Igniting gunpowder.Bore a hole one-half inch in diameter and one inch deep in a block of hardwood. Pass two small brass wires through holes in the sides, letting the ends of the wires be about one-eighth of an inch apart. Pour a little gunpowder in loosely over the wires. Tie a piece of thoroughly moistened cotton twine, three inches long, to one of the wires and attach it to the outside coating of a charged Leyden jar.
Connect the knob of the jar to the other wire. The gunpowder will immediately explode. Keep the face and hands away from the gunpowder when performing this experiment.
Fig. 47.—An Electric Umbrella.Fig. 47.—An Electric Umbrella.
Fig. 47.—An Electric Umbrella.
Electric Umbrella.The repulsion of similarly electrified bodies which was illustrated by the action of the pith ball electroscope may be better illustrated by pasting some narrow streamers of tissue paper about one-eighth of an inch wide and four inches long to a small cork covered with tinfoil. The cork is mounted on the upper end of a stiff copper wire supported in a bottle. When the wire is connected to the prime conductor and the machine set in motion, the strips will spread out like an umbrella.
Lightning Board.A pane of glass is thoroughly cleaned and then given a coat of shellac or varnish. Before the varnish is dry, press on a piece of tinfoil large enough to cover one side of the glass and rub it down smoothly.
Fig. 48.—A Lightning Board.Fig. 48.—A Lightning Board.
Fig. 48.—A Lightning Board.
After the shellac or varnish is dry, cut the tinfoil up into innumerable little squares with a sharp knife and ruler, leaving two solid strips of tinfoil at the ends of the glass pane.
The pane is mounted by cementing it in a slot in the cork of a bottle. Connect one of the tinfoil strips to the prime conductor and the other to the earth or the body. When the machine is turned, innumerable little sparks will pass between the tinfoil squares and give an appearance very similar to that of lightning.
Fig. 49.—An Electric Dance.Fig. 49.—An Electric Dance.
Fig. 49.—An Electric Dance.
The Electrical Dance.A number of little balls of cork or pith are enclosed in a cylinder of glass about two and one-half or three inches high formed by cutting off the top of a lamp chimney. The top and bottom of the cylinder are closed by two circular pieces of sheet brass or copper. The top disk is connected to the prime conductor while the bottom one is connected to the rubber. When the machine is set in motion, the little balls will dance up and down. Bits of feather or paper cut to represent figures of men and women may be used as well as pith or cork balls.
The Electric Whirl.The whirl consists of an S shaped piece of brass wire, pointed at both ends and supported on a needle by a little conical depression made in the center with a punch.
Fig. 50.—An Electric Whirl.Fig. 50.—An Electric Whirl.
Fig. 50.—An Electric Whirl.
The needle is stuck in a cork in the top of a bottle and connected with the prime conductor of the electric machine. When the latter is set in motion, the whirl will commence to revolve at a high rate of speed.
Lichtenberg’s Figurescan be produced by charging a Leyden jar by connecting the knob or inside coating with the prime conductor and holding the outside coating in the hand.
Then trace a small circle on the electrophorus bed with the knob.
Charge a second Leyden jar by connecting the outside coating with the prime conductor.
The inside coating should be connected to the rubber by means of a wire fastened to the knob. The same result may be obtained by connecting the outside coating with the prime conductor and touching the knob with the hand.
Then trace a cross on the electrophorus bed with the knob, making the cross inside of the circle.
Fig. 51.—Lichtenberg's Figures.Fig. 51.—Lichtenberg's Figures.
Fig. 51.—Lichtenberg's Figures.
Shake a mixture of red lead and sulphur through a muslin bag from a height of several inches over the electrophorus.
The red lead will accumulate around the cross and the sulphur around the circle.
CELLS AND BATTERIES