Fig. 69. Trammel Fig. 70. Escapement Fig. 71. Device for Holding Wheel Fig. 72. Rack and Pinion Fig. 73. Mutilated Gears Fig. 74. Shaft CouplingToListFig. 69.Trammel for Making an Ellipse.—This is a tool easily made, which will be of great service in the shop. In a disc (A), preferably made of brass, are two channels (B) at right angles to each other. The grooves are undercut, so that the blocks (C) will fit and slide in the grooves and be held therein by the dove-tailed formation. Each block is longer than the width of the groove, and has an outwardly projecting pin which passes through a bar (D). One pin (E) is movable along in a slot, but is adjustable at any point so that the shape of the ellipse may bep. 71varied. The end of the bar has a series of holes (G) for a pencil, so that the size of the ellipse may also be changed.Fig. 70.Escapements.—Various forms of escapements may be made, but the object of all is the same. The device is designed to permit a wheel to move intermittingly or in a step by step movement, by the swinging motion of a pendulum. Another thing is accomplished by it. The teeth of the escapement are cut at such an angle that, as one of the teeth of the escapement is released from one tooth of the escapement wheel, the spring, or the weight of the clock, will cause one of the teeth of the escapement wheel to engage the other tooth of the escapement, and give the pendulum an impulse in the other direction. In the figure, A is the escapement, B the escapement wheels anda,b, thep. 72pallets, which are cut at suitable angles to actuate the pendulum.Fig. 71.Simple Device to Prevent a Wheel or Shaft prom Turning Back.—This is a substitute for a pawl and ratchet wheel. A is a drum or a hollow wheel and B a pulley on a shaft, and this pulley turns loosely with the drum (A). Four tangential slots (C) are cut into the perimeter of the pulley (B), and in each is a hardened steel roller (D). It matters not in what position the wheel (B) may be, at least two of the rollers will always be in contact with the inside of the drum (A), and thus cause the pulley and drum to turn together. On reversing the direction of the pulley the rollers are immediately freed from binding contact.Fig. 72.Racks and Pinions.—The object of this form of mechanism is to provide a reciprocating, or back-and-forth motion, from a shaft which turns continually in one direction. A is the rack and B a mutilated gear. When the gear turns it moves the rack in one direction, because the teeth of the gear engage the lower rack teeth, and when the rack has moved to the end its teeth engage the teeth of the upper rack, thus reversing the movement of the rack.Fig. 73.Mutilated Gears.—These are made in so many forms, and adapted for such ap. 73variety of purposes, that we merely give a few samples to show what is meant by the term.Fig. 74.Simple Shaft Coupling.—Prepare two similarly formed discs (A, B), which are provided with hubs so they may be keyed to the ends of the respective shafts. One disc has four or more projecting pins (C), and the other disc suitable holes (D) to receive the pins.
Fig. 69. Trammel Fig. 70. Escapement Fig. 71. Device for Holding Wheel Fig. 72. Rack and Pinion Fig. 73. Mutilated Gears Fig. 74. Shaft CouplingToList
Fig. 69.Trammel for Making an Ellipse.—This is a tool easily made, which will be of great service in the shop. In a disc (A), preferably made of brass, are two channels (B) at right angles to each other. The grooves are undercut, so that the blocks (C) will fit and slide in the grooves and be held therein by the dove-tailed formation. Each block is longer than the width of the groove, and has an outwardly projecting pin which passes through a bar (D). One pin (E) is movable along in a slot, but is adjustable at any point so that the shape of the ellipse may bep. 71varied. The end of the bar has a series of holes (G) for a pencil, so that the size of the ellipse may also be changed.
Fig. 70.Escapements.—Various forms of escapements may be made, but the object of all is the same. The device is designed to permit a wheel to move intermittingly or in a step by step movement, by the swinging motion of a pendulum. Another thing is accomplished by it. The teeth of the escapement are cut at such an angle that, as one of the teeth of the escapement is released from one tooth of the escapement wheel, the spring, or the weight of the clock, will cause one of the teeth of the escapement wheel to engage the other tooth of the escapement, and give the pendulum an impulse in the other direction. In the figure, A is the escapement, B the escapement wheels anda,b, thep. 72pallets, which are cut at suitable angles to actuate the pendulum.
Fig. 71.Simple Device to Prevent a Wheel or Shaft prom Turning Back.—This is a substitute for a pawl and ratchet wheel. A is a drum or a hollow wheel and B a pulley on a shaft, and this pulley turns loosely with the drum (A). Four tangential slots (C) are cut into the perimeter of the pulley (B), and in each is a hardened steel roller (D). It matters not in what position the wheel (B) may be, at least two of the rollers will always be in contact with the inside of the drum (A), and thus cause the pulley and drum to turn together. On reversing the direction of the pulley the rollers are immediately freed from binding contact.
Fig. 72.Racks and Pinions.—The object of this form of mechanism is to provide a reciprocating, or back-and-forth motion, from a shaft which turns continually in one direction. A is the rack and B a mutilated gear. When the gear turns it moves the rack in one direction, because the teeth of the gear engage the lower rack teeth, and when the rack has moved to the end its teeth engage the teeth of the upper rack, thus reversing the movement of the rack.
Fig. 73.Mutilated Gears.—These are made in so many forms, and adapted for such ap. 73variety of purposes, that we merely give a few samples to show what is meant by the term.
Fig. 74.Simple Shaft Coupling.—Prepare two similarly formed discs (A, B), which are provided with hubs so they may be keyed to the ends of the respective shafts. One disc has four or more projecting pins (C), and the other disc suitable holes (D) to receive the pins.
Fig. 75. Clutches Fig. 76. Ball and Socket Joints Fig. 77. Fastening Ball Fig. 78. Tripping Devices Fig. 79. Anchor Bolt Fig. 80. Lazy Tongs. Fig. 81. Disc Shears.ToListFig. 75.Clutches.—This is a piece of mechanism which is required in so many kinds of machinery, that we show several of the most approved types.Fig. 76.Ball and Socket Joints.—The most practical form of ball and socket joints is simply a head in which is a bowl-shaped cavity the depth of one-half of the ball. A plate with a central opening small enough to hold in the ball, andp. 74still large enough at the neck to permit the arm carrying the ball to swing a limited distance, is secured by threads, or by bolts, to the head. The first figure shows this.Fig. 77illustrates a simple manner of tightening the ball so as to hold the standard in any desired position.Fig. 78.Tripping Devices.—These are usually in the form of hooks, so arranged that a slight pull on the tripping lever will cause the suspended articles to drop.Fig. 79.Anchor Bolt.—These are used in brick or cement walls. The bolt itself screws into a sleeve which is split, and draws a wedge nut up to the split end of the sleeve. As a result the split sleeve opens or spreads out and binds against the wall sufficiently to prevent the bolt from being withdrawn.Fig. 80.Lazy Tongs.—One of the simplest and most effective instruments for carrying ice, boxes or heavy objects, which are bulky or inconvenient to carry. It grasps the article firmly, and the heavier the weight the tighter is its grasp.Fig. 81.Disc Shears.—This is a useful tool either for cutting tin or paper, pasteboard and the like. It will cut by the act of drawing the material through it, but if power is applied to one or to both of the shafts the work is much facilitated,p. 75particularly in thick or hard material.
Fig. 75. Clutches Fig. 76. Ball and Socket Joints Fig. 77. Fastening Ball Fig. 78. Tripping Devices Fig. 79. Anchor Bolt Fig. 80. Lazy Tongs. Fig. 81. Disc Shears.ToList
Fig. 75.Clutches.—This is a piece of mechanism which is required in so many kinds of machinery, that we show several of the most approved types.
Fig. 76.Ball and Socket Joints.—The most practical form of ball and socket joints is simply a head in which is a bowl-shaped cavity the depth of one-half of the ball. A plate with a central opening small enough to hold in the ball, andp. 74still large enough at the neck to permit the arm carrying the ball to swing a limited distance, is secured by threads, or by bolts, to the head. The first figure shows this.
Fig. 77illustrates a simple manner of tightening the ball so as to hold the standard in any desired position.
Fig. 78.Tripping Devices.—These are usually in the form of hooks, so arranged that a slight pull on the tripping lever will cause the suspended articles to drop.
Fig. 79.Anchor Bolt.—These are used in brick or cement walls. The bolt itself screws into a sleeve which is split, and draws a wedge nut up to the split end of the sleeve. As a result the split sleeve opens or spreads out and binds against the wall sufficiently to prevent the bolt from being withdrawn.
Fig. 80.Lazy Tongs.—One of the simplest and most effective instruments for carrying ice, boxes or heavy objects, which are bulky or inconvenient to carry. It grasps the article firmly, and the heavier the weight the tighter is its grasp.
Fig. 81.Disc Shears.—This is a useful tool either for cutting tin or paper, pasteboard and the like. It will cut by the act of drawing the material through it, but if power is applied to one or to both of the shafts the work is much facilitated,p. 75particularly in thick or hard material.
Fig. 82. Wabble Saw Fig. 83. Continuous Crank Motion Fig. 84. Continuous Feed Fig. 85. Crank Motion Fig. 86. Ratchet Head Fig. 87. Bench ClampToListFig. 82.Wabble Saw.—This is a most simple and useful tool, as it will readily and quickly saw out a groove so that it is undercut. The saw is put on the mandrel at an angle, as will be seen, and should be run at a high rate of speed.Fig. 83.Crank Motion by a Slotted Yoke.—This produces a straight back-and-forth movement from the circular motion of a wheel or crank. It entirely dispenses with a pitman rod, and it enables the machine, or the part of the machine operated, to be placed close to the crank.Fig. 84.Continuous Feed by the Motion of a Lever.—The simple lever with a pawl on each side of the fulcrum is the most effective means to make a continuous feed by the simple movement of a lever. The form shown is capable ofp. 76many modifications, and it can be easily adapted for any particular work desired.Fig. 85.Crank Motion.—By the structure shown, namely, a slotted lever (A), a quick return can be made with the lever. B indicates the fulcrum.Fig. 86.Ratchet Head.—This shows a well-known form for common ratchet. It has the advantage that the radially movable plugs (A) are tangentially disposed, and rest against walls (B) eccentrically disposed, and are, therefore, in such a position that they easily slide over the inclines.Fig. 87.Bench Clamp.—A pair of dogs (A, B), with the ends bent toward each other, and pivoted midway between the ends to the bench in such a position that the board (C), to be held between them, on striking the rear ends of the dogs, will force the forward ends together, and thus clampp. 77it firmly for planing or other purposes.
Fig. 82. Wabble Saw Fig. 83. Continuous Crank Motion Fig. 84. Continuous Feed Fig. 85. Crank Motion Fig. 86. Ratchet Head Fig. 87. Bench ClampToList
Fig. 82.Wabble Saw.—This is a most simple and useful tool, as it will readily and quickly saw out a groove so that it is undercut. The saw is put on the mandrel at an angle, as will be seen, and should be run at a high rate of speed.
Fig. 83.Crank Motion by a Slotted Yoke.—This produces a straight back-and-forth movement from the circular motion of a wheel or crank. It entirely dispenses with a pitman rod, and it enables the machine, or the part of the machine operated, to be placed close to the crank.
Fig. 84.Continuous Feed by the Motion of a Lever.—The simple lever with a pawl on each side of the fulcrum is the most effective means to make a continuous feed by the simple movement of a lever. The form shown is capable ofp. 76many modifications, and it can be easily adapted for any particular work desired.
Fig. 85.Crank Motion.—By the structure shown, namely, a slotted lever (A), a quick return can be made with the lever. B indicates the fulcrum.
Fig. 86.Ratchet Head.—This shows a well-known form for common ratchet. It has the advantage that the radially movable plugs (A) are tangentially disposed, and rest against walls (B) eccentrically disposed, and are, therefore, in such a position that they easily slide over the inclines.
Fig. 87.Bench Clamp.—A pair of dogs (A, B), with the ends bent toward each other, and pivoted midway between the ends to the bench in such a position that the board (C), to be held between them, on striking the rear ends of the dogs, will force the forward ends together, and thus clampp. 77it firmly for planing or other purposes.
Fig. 88. Helico-Volute Spring Fig. 89. Double Helico-Volute Fig. 90. Helical Spring Fig. 91. Single Volute Helix-Spring Fig. 92. Flat Spiral or Convolute Fig. 93. Eccentric Rod and Strap Fig. 94. Anti-Dead Center for Foot-LathesToListFig. 88.Helico-Volute Spring.—This is a form of spring for tension purposes. The enlarged cross-section of the coil in its middle portion, with the ends tapering down to the eyes, provides a means whereby the pull is transferred from the smaller to the larger portions, without producing a great breaking strain near the ends.Fig. 89.Double Helico-Volute.—This form, so far as the outlines are considered, is the opposite ofFig. 88. A compression spring of this kind has a very wide range of movement.Fig. 90.Helical Spring.—This form of coil, uniform from end to end, is usually made of metal which is square in cross-section, and used where it is required for heavy purposesp. 78Fig. 91.Single Volute Helix-Spring.—This is also used for compression, intended where tremendous weights or resistances are to be overcome, and when the range of movement is small.Fig. 92.Flat Spiral, or Convolute.—This is for small machines. It is the familiar form used in watches owing to its delicate structure, and it is admirably adapted to yield to the rocking motion of an arbor.Fig. 93.Eccentric Rod and Strap.—A simple and convenient form of structure, intended to furnish a reciprocating motion where a crank is not available. An illustration of its use is shown on certain types of steam engine to operate the valves.Fig. 94.Anti-Dead Center for Foot-Lathes.—A flat, spiral spring (A), with its coiled end attached to firm support (B), has its other end pivotally attached to the crank-pin (C), the tension of the spring being such that when the lathe stops the crack-pin will always be at one side of the dead-center, thus enabling the operator to start the machine by merely pressing the foot downwardly on the treadle (D)
Fig. 88. Helico-Volute Spring Fig. 89. Double Helico-Volute Fig. 90. Helical Spring Fig. 91. Single Volute Helix-Spring Fig. 92. Flat Spiral or Convolute Fig. 93. Eccentric Rod and Strap Fig. 94. Anti-Dead Center for Foot-LathesToList
Fig. 88.Helico-Volute Spring.—This is a form of spring for tension purposes. The enlarged cross-section of the coil in its middle portion, with the ends tapering down to the eyes, provides a means whereby the pull is transferred from the smaller to the larger portions, without producing a great breaking strain near the ends.
Fig. 89.Double Helico-Volute.—This form, so far as the outlines are considered, is the opposite ofFig. 88. A compression spring of this kind has a very wide range of movement.
Fig. 90.Helical Spring.—This form of coil, uniform from end to end, is usually made of metal which is square in cross-section, and used where it is required for heavy purposes
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Fig. 91.Single Volute Helix-Spring.—This is also used for compression, intended where tremendous weights or resistances are to be overcome, and when the range of movement is small.
Fig. 92.Flat Spiral, or Convolute.—This is for small machines. It is the familiar form used in watches owing to its delicate structure, and it is admirably adapted to yield to the rocking motion of an arbor.
Fig. 93.Eccentric Rod and Strap.—A simple and convenient form of structure, intended to furnish a reciprocating motion where a crank is not available. An illustration of its use is shown on certain types of steam engine to operate the valves.
Fig. 94.Anti-Dead Center for Foot-Lathes.—A flat, spiral spring (A), with its coiled end attached to firm support (B), has its other end pivotally attached to the crank-pin (C), the tension of the spring being such that when the lathe stops the crack-pin will always be at one side of the dead-center, thus enabling the operator to start the machine by merely pressing the foot downwardly on the treadle (D)
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A workman is able to select the right metals because he knows that each has some peculiar property which is best adapted for his particular use. These with their meaning will now be explained.
Elasticity.—This exists in metals in three distinct ways: First, in the form oftraction. Hang a weight on a wire and it will stretch a certain amount. When the weight is removed the wire shrinks back to its original length.
Second: If the weight on the wire is rotated, so as to twist it, and the hand is taken from the weight, it will untwist itself, and go back to its original position. This is calledtorsion.
Third: A piece of metal may be coiled up like a watch spring, or bent like a carriage spring, and it will yield when pressure is applied. This is calledflexure.
Certain kinds of steel have these qualities in a high degree.
Tenacity.—This is a term used to express the resistance which the body opposes to the separation of its parts. It is determined by formingp. 80the metal into a wire, and hanging on weights, to find how much will be required to break it. If we have two wires, the first with a transverse area only one-quarter that of the second, and the first breaks at 25 pounds, while the second breaks at 50 pounds, the tenacity of the first is twice as great as that of the second.
To the boy who understands simple ratio in mathematics, the problem would be like this:
25 × 4 : 50 × 1, or as 2 : 1.
The Most Tenacious Metal.—Steel has the greatest tenacity of all metals, and lead the least. In proportion to weight, however, there are many substances which have this property in a higher degree. Cotton fibers will support millions of times their own weight.
There is one peculiar thing, that tenacity varies with the form of the body. A solid cylindrical body has a greater strength than a square one of the same size; and a hollow cylinder more tenacity than a solid one. This principle is well known in the bones of animals, in the feathers of birds, and in the stems of many plants.
In almost every metal tenacity diminishes as the temperature increases.
Ductility.—This is a property whereby a metal may be drawn out to form a wire. Some metals,p. 81like cast iron, have absolutely no ductility. The metal which possesses this property to the highest degree, is platinum. Wires of this metal have been drawn out so fine that over 30,000 of them laid side by side would measure only one inch across, and a mile of such wire would weigh only a grain, or one seven-thousandth of a pound.
Malleability.—This is considered a modification of ductility. Any metal which can be beaten out, as with a hammer, or flattened into sheets with rollers, is considered malleable. Gold possesses this property to the highest degree. It has been beaten into leaves one three-hundred-thousandth of an inch thick.
Hardness.—This is the resistance which bodies offer to being scratched by others. As an example, the diamond has the capacity to scratch all, but cannot be scratched by any other.
Alloys.—Alloys, that is a combination of two or more metals, are harder than the pure metals, and for this reason jewelry, and coins, are usually alloyed.
The resistance of a body to compression does not depend upon its hardness. Strike a diamond with a hammer and it flies to pieces, but wood does not. One is brittle and the other is tough.
The machinist can utilize this property by understanding that velocity enables a soft materialp. 82to cut a harder one. Thus, a wrought iron disc rotating rapidly, will cut such hard substances as agate or quartz.
Resistance.—All metals offer more or less resistance to the flow of an electric current. Silver offers the least resistance, and German silver the greatest. Temperature also affects the flow. It passes more easily over a cold than a warm conductor.
Persistence.—All metals on receiving heat, will retain it for a certain length of time, and will finally cool down to the temperature of the surrounding atmosphere. Some, like aluminum, retain it for a long time; others, as iron, will give it off quickly.
Conductivity.—All metals will conduct heat and cold, as well as electricity. If one end of a metal bar is heated, the heat creeps along to the other end until it has the same temperature throughout. This is calledequalization.
If a heated bar is placed in contact with another, the effect is to increase the temperature of the cold bar and lower that of the warm bar. This is calledreciprocity.
Molecular Forces.—Molecularattraction is a force which acts in such a way as to bring all the particles of a body together. It acts in threep. 83ways, dependent on the particular conditions which exist.
First:Cohesion. This exists between molecules which are of the same kind, as for instance, iron. Cohesion of the particles is very strong in solids, much weaker in liquids, and scarcely exists at all between the particles in gases.
Second:Adhesionis that property which exists between the surfaces of bodies in contact. If two flat surfaces are pressed together, as for instance, two perfectly smooth and flat pieces of lead, they will adhere. If, for instance, oil should be put on the surfaces, before putting them together, they would adhere so firmly that it would be difficult to pull them apart.
Third:Affinity. This is another peculiarity about materials. Thus, while cohesion binds together the molecules of water, it is chemical affinity which unites two elements, like hydrogen and oxygen, of which water is composed.
Porosity.—All matter has little hollows or spaces between the molecules. You know what this is in the case of a sponge, or pumice stone. Certain metals have the pores so small that it is difficult to see them except with a very powerful glass. Under great pressure water can be forced through the pores of metals, as has been done inp. 84the case of gold. Water also is porous, but the spaces between the molecules are very small.
Compressibility.—It follows from the foregoing statement, that if there are little interstices between the molecules, the various bodies can be compressed together. This can be done in varying degrees with all solids, but liquids, generally, have little compressibility. Gases are readily reduced in volume by compression.
Elasticity.—This is a property by virtue of which a body resumes its original form when compressed. India rubber, ivory and glass are examples of elasticity; whereas, lead and clay do not possess this property. Air is the most elastic of all substances.
Inertia.—This is a property of matter by virtue of which it cannot of itself change its state of motion or of rest.
Newton's first law of motion is, in substance, that matter at rest will eternally remain at rest, and matter in motion will forever continue in motion, unless acted on by some external force.
A rider is carried over the head of a horse when the latter suddenly stops. This illustrates the inertia of movement. A stone at rest will always remain in that condition unless moved by some force. That shows the inertia of rest.
Momentum.—This is the term to designate thep. 85quantity of motion in a body. This quantity varies and is dependent on the mass, together with the velocity. A fly wheel is a good example. It continues to move after the impelling force ceases; and a metal wheel has greater momentum than a wooden wheel at the same speed, owing to its greater mass.
If, however, the wooden wheel is speeded up sufficiently it may have the same momentum as the metal one.
Weight.—All substances have what is calledweight. This means that everything is attracted toward the earth by the force of gravity. Gravity, however, is different from weight. All substances attract each other; not only in the direction of the center of the earth, but laterally, as well.
Weight, therefore, has reference to the pull of an object toward the earth; and gravity to that influence which all matter has for each other independently of the direction.
Centripetal Force.—This attraction of the earth, which gives articles the property of weight, is termed centripetal force—that is, the drawing in of a body.
Centrifugal Force.—The direct opposite of centripetal, is centrifugal force, which tends top. 86throw outwardly. Dirt flying from a rapidly moving wheel illustrates this.
Capillary Attraction.—There is a peculiar property in liquids, which deserves attention, and should be understood, and that is the name given to the tendency of liquids to rise in fine tubes.
It is stated that water will always find its level. While this is true, we have an instance where, owing to the presence of a solid, made in a peculiar form, causes the liquid, within, to rise up far beyond the level of the water.
This may be illustrated by three tubes of different internal diameters. The liquid rises up higher in the second than in the first, and still higher in the third than in the second. The smaller the tube the greater the height of the liquid.
This is calledcapillary attraction, the word capillary meaning a hair. The phenomena is best observed when seen in tubes which are as fine as hairs. The liquid has an affinity for the metal, and creeps up the inside, and the distance it will thus move depends on the size of the tube.
The Sap of Trees.—The sap of trees goes upwardly, not because the tree is alive, but due to this property in the contact of liquids with a solid. It is exactly on the same principle that if the end of a piece of blotting paper is immersedp. 87in water, the latter will creep up and spread over the entire surface of the sheet.
In like manner, oil moves upwardly in a wick, and will keep on doing so, until the lighted wick is extinguished, when the flow ceases. When it is again lighted the oil again flows, as before.
If it were not for this principle of capillary attraction, it would be difficult to form a bubble of air in a spirit level. You can readily see how the liquid at each end of the air bubble rounds it off, as though it tried to surround it.
Sound.—Sound is caused by vibration, and it would be impossible to convey it without an elastic medium of some kind.
Acousticsis a branch of physics which treats of sounds. It is distinguished from music which has reference to the particular kinds.
Soundsare distinguished fromnoises. The latter are discordant and abrupt vibrations, whereas the former are regular and continuous.
Sound Mediums.—- Gases, vapors, liquids and solids transmit vibrations, but liquids and solids propagate with greater velocity than gases.
Vibration.—A vibration is the moving to and fro of the molecules in a body, and the greater their movement the more intense is the sound. The intensity of the sound is affected by the density of the atmosphere, and the movementp. 88of the winds also changes its power of transmission.
Sound is also made more intense if a sonorous body is near its source. This is taken advantage of in musical instruments, where a sounding-board is used, as in the case of the piano, and in the violin, which has a thin shell as a body for holding the strings.
Another curious thing is shown in the speaking tube, where the sound waves are confined, so that they are carried along in one line, and as they are not interfered with will transmit the vibrations to great distances.
Velocity of Sound.—The temperature of the air has also an effect on the rate of transmission, but for general purposes a temperature of 62 degrees has been taken as the standard. The movement is shown to be about 50 miles in 4 minutes, or at the rate of 1,120 feet per second.
In water, however, the speed is four times greater; and in iron nearly fifteen times greater. Soft earth is a poor conductor, while rock and solid earth convey very readily. Placing the ear on a railway track will give the vibrations of a moving train miles before it can be heard through the air.
Sound Reflections.—Sound waves move outwardly from the object in the form of wave-likep. 89rings, but those concentric rings, as they are called, may be interrupted at various points by obstacles. When that is the case the sound is buffeted back, producing what is called echoes.
Resonance.—Materials have a quality that produces a very useful result, calledresonance, and it is one of the things that gives added effect to a speaker's voice in a hall, where there is a constant succession of echoes. A wall distant from the speaker about 55 feet, produces an almost instantaneous reflection of the sound, and at double that measurement the effect is still stronger. When the distance is too short for the reflecting sound to be heard, we haveresonance. It enriches the sound of the voice, and gives a finer quality to musical instruments.
Echoes.—When sounds are heard after the originals are emitted they tend to confusion, and the quality of resonance is lost. There are places where echoes are repeated many times. In the chateau of Simonetta, Italy, a sound will be repeated thirty times.
Speaking Trumpet.—This instrument is an example of the use of reflection. It is merely a bell-shaped, or flaring body, the large end of which is directed to the audience. The voice talking into the small end is directed forwardly, and is reflected from the sides, and its resonance also enables thep. 90vibrations to carry farther than without the use of the solid part of the instrument.
The ear trumpet is an illustration of a sound-collecting device, the waves being brought together by reflection.
The Stethoscope.—This is an instrument used by physicians, and it is so delicate that the movements of the organs of the body can be heard with great distinctness. It merely collects the vibrations, and transmits them to the ears by the small tubes which are connected with the collecting bell.
The Vitascope.—- Numerous instruments have been devised to determine the rate of vibration of different materials and structures, the most important being thevitascope, which has a revolvable cylinder, blackened with soot, and this being rotated at a certain speed, the stylus, which is attached to the vibrating body, in contact with the cylinder, will show the number per second, as well as the particular character of each oscillation.
The Phonautograph.—This instrument is used to register the vibration of wind instruments, as well as the human voice, and the particular forms of the vibrations are traced on a cylinder, the tracing stylus being attached to a thin vibrating membrane which is affected by the voice or instrument.
The Phonograph.—This instrument is the outgrowth of the stylus forms of the apparatus dep. 91scribed, but in this case the stylus, or needle, is fixed to a metallic diaphragm, and its point makes an impression on suitable material placed on the outside of a revolvable cylinder or disc.
Light.-Light is the agent which excites the sensation of vision in the eye. Various theories have been advanced by scientists to account for the phenomenon, and the two most noted views are thecorpuscular, promulgated by Sir Isaac Newton, and theundulatory, enunciated by Huygens and Euler.
Thecorpusculartheory conceives that light is a substance of exceedingly light particles which are shot forth with immense velocity. Theundulatorytheory, now generally accepted, maintains that light is carried by vibrations in ether. Ether is a subtle elastic medium which fills all space.
Luminousbodies are those like the sun, which emit light. Rays maydiverge, that is, spread out;converge, or point toward each other; or they may beparallelwith each other.
Velocity of Light.—Light moves at the rate of about 186,000 miles a second. As the sun is about 94,000,000 miles from the earth, it takes 81/2minutes for the light of the sun to reach us.
Reflection.—One of the most important things connected with light is that of reflection. It is that quality which is utilized in telescopes, microp. 92scopes, mirrors, heliograph signaling and other like apparatus and uses. The underlying principle is, that a ray is reflected, or thrown back from a mirror at the same angle as that which produces the light.
When the rays of the sun, which are, of course, parallel, strike a concave mirror, the reflecting rays are converged; and when the rays strike a convex mirror they diverge. In this way the principle is employed in reflecting telescopes.
Refraction.—This is the peculiar action of light in passing through substances. If a ray passes through water at an angle to the surface the ray will bend downwardly in passing through, and then again pass on in a straight line. This will be noticed if a pencil is stood in a glass of water at an angle, when it will appear bent.
Refraction is that which enables light to be divided up, or analyzed. In this way white light from the sun is shown to be composed of seven principal colors.
Colors.—If the light is passed through a prism, which is a triangularly shaped piece of glass, the rays on emerging will diverge from each other, and when they fall on a wall or screen the colors red, orange, yellow, green, blue, indigo and violet are shown
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The reason for this is that the ray in passing through the prism has the different colors in it refract at different angles, the violet bending more than the red.
The Spectroscope.—The ability to make what is thus called aspectrum, brought forth one of the most wonderful instruments ever devised by man. If any metal, or material, is fused, or put in such a condition that a ray of light can be obtained from it, and this light is passed through a prism, it will be found that each substance has its own peculiar divisions and arrangements of colors.
In this way substances are determined by what is calledspectrum analysis, and it is by means of this instrument that the composition of the sun, and the planets and fixed stars are determined.
The Rainbow.—The rainbow is one of the effects of refraction, as the light, striking the little globular particles of water suspended in the air, produces a breaking up of the white light into its component colors, and the sky serves as a background for viewing the analysis thus made.
Heat.—It is now conclusively proven, that heat, like light, magnetism and electricity, is merely a mode of motion.
Themechanicaltheory of heat may be shown by rubbing together several bodies. Heat expandsp. 94all substances, except ice, and in expanding develops an enormous force.
Expansion.—In like manner liquids expand with heat. The power of mercury in expanding may be understood when it is stated that a pressure of 10,000 pounds would be required to prevent the expansion of mercury, when heated simply 10 degrees.
Gases also expand. While water, and the different solids, all have their particular units of expansion, it is not so with gases, as all have the same coefficient
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The ability to read drawings is a necessary part of the boy's education. To know how to use the tools, is still more important. In conveying an idea about a piece of mechanism, a sketch is given. Now, the sketch may be readable in itself, requiring no explanation, or it may be of such a nature that it will necessitate some written description.
Fig. 95. Plain CircleFig. 95. Plain CircleToList
Lines in Drawing.—- In drawing, lines have a definite meaning. A plain circular line, likeFig. 95, when drawn in that way, conveys three meanings: It may represent a rim, or a bent piece of wire; it may illustrate a disk; or, it may convey the idea of a ball.
Suppose we develop them to express the three forms accurately.Fig. 96, by merely adding anp. 96interior line, shows that it is a rim. There can be no further doubt about that expression.
Fig. 97shows a single line, but it will now be noticed that the line is thickened at the lower right-hand side, and from this you can readily infer that it is a disk.
Shading.—Fig. 98, by having a few shaded lines on the right and lower side, makes it have the appearance of a globe or a convex surface.
Figs. 96-98. Ring - Raised Surface - SphereFigs. 96-98.Ring - Raised Surface - SphereToList
Shading or thickening the lines also gives another expression to the same circular line.
InFig. 99, if the upper and left-hand side of the circle is heavily shaded, it shows that the area within the circle is depressed, instead of being raised.
Direction of Shade.—On the other hand, if the shading lines, as inFig. 100, are at the upper left-hand side, then the mind at once grasps the idea of a concave surface.
The first thing, therefore, to keep in mind, is thisp. 97fact: That in all mechanical drawing, the light is supposed to shine down from the upper left-hand corner and that, as a result, the lower vertical line, as well as the extreme right-hand vertical line, casts the shadows, and should, therefore, be made heavier than the upper horizontal, and the left-hand vertical lines.
Fig. 99. Depressed Surface Fig. 100. ConcaveFigs. 99-100.Depressed Surface - ConcaveToList
There are exceptions to this rule, which will be readily understood by following out the illustrations in the order given below.
Perspectives.—The utility of the heavy lines will be more apparent when drawing square, rectangular, or triangular objects.
Let us takeFig. 101, which appears to be the perspective of a cube. Notice that all lines are of the same thickness. When the sketch was first brought to me I thought it was a cube; but the explanation which followed, showed that the man whop. 98made the sketch had an entirely different meaning.
He had intended to convey to my mind the idea of three pieces, A, B, C, of metal, of equal size, joined together so as to form a triangularly shaped pocket as shown inFig. 101. The addition of the inner lines, like D, quickly dispelled the suggestion of the cube.
Figs. 101-104. Forms of Cubical OutlinesFigs. 101-104. Forms of Cubical OutlinesToList
"But," he remarked, "I want to use the thinnest metal, like sheets of tin; and you show them thick by adding the inner lines."
Such being the case, if we did not want to showp. 99thickness as its structural form, we had to do it by making the lines themselves and the shading give that structural idea. This was done by using the single lines, as inFig. 103, and by a slight shading of the pieces A, B, C.
The Most Pronounced Lines.—If it had been a cube, or a solid block, the corners nearest the eye would have been most pronounced, as inFig. 104, and the side next to the observer would have been darkest.
This question of light and shadow is what expresses the surface formation of every drawing. Simple strokes form outlines of the object, but their thickness, and the shading, show the character enclosed by the lines.p. 100Direction of Light.—Now, as stated, the casting of the shadow downward from the upper left-hand corner makes the last line over which it passes the thickest, and inFigs. 105and106they are not the extreme lines at the bottom and at the right side, because of the close parallel lines.
InFigs. 109and110the blades superposed on the other are very thin, and the result is the lines at the right side and bottom are made much heavier.
This is more fully shown inFigs. 107and108. Notice the marked difference between the two figures, both of which show the same set of pulleys, and the last figure, by merely having the lower and the right-hand lines of each pulley heavy, changes the character of the representation, and tells much more clearly what the draughtsman sought to convey.
Scale Drawings.—All drawings are made to ap. 101scale where the article is large and cannot be indicated the exact size, using parts of an inch to represent inches; and parts of a foot to represent feet.
In order to reduce a drawing where a foot is the unit, it is always best to use one-and-a-half inches, or twelve-eighths of an inch, as the basis. In this way each eighth of an inch represents an inch. If the drawing should be made larger, then use three inches, and in that way each inch would be one-quarter of an inch.
The drawing should then have marked, in some conspicuous place, the scale, like the following: "Scale, 11/2" = 1'"; or, "Scale 3" = 1'."
Degree, and What it Means.—A degree is notp. 102a measurement. The word is used to designate an interval, a position, or an angle. Every circle has 360 degrees, and when a certain degree is mentioned, it means a certain angle from what is called abase line.