TO EXHIBIT THE MAGIC LANTERN.
The room for the exhibition ought to be large, and of an oblong shape. At one end of it suspend a large sheet so as to cover the whole of the wall. The company being all seated, darken the room, and placing the lantern with its tube in the direction of the sheet, introduce one of the slides into the slit, taking care to invert the figures; then adjust the focus of the glasses in the tube by drawing it in or out as required, and a perfect representation of the object will appear.
EFFECTS OF THE MAGIC LANTERN.
Most extraordinary effects may be produced by means of the magic lantern; one of the most effective of which is a
TEMPEST AT SEA.
This is effected by having two slides painted, one with the tempest as approaching on one side, and continuing in intensity till it reaches the other. Another slide has shipspainted on it, and while the lantern is in use, that containing the ships is dexterously drawn before the other, and representsships in the storm.
The effects of sunrise, moonlight, starlight, &c., may be imitated, also by means of double sliders; and figures may be introduced sometimes of fearful proportions.
Heads may be made to nod, faces to laugh; eyes may be made to roll, teeth to gnash; crocodiles may be made to swallow tigers; combats may be represented; but one of the most instructive uses of the slides is to make them illustrative of astronomy, and to show the rotation of the seasons, the cause of eclipses, the mountains in the moon, spots on the sun, and the various motions of the planetary bodies, and their satellites.
THE PHANTASMAGORIA.
Between the phantasmagoria and the magic lantern there is this difference; in common magic lanterns the figures are painted on transparent glass, consequently the image on the screen is a circle of light having figures upon it; but in the phantasmagoria all the glass is made opaque, except the figures, which, being painted in transparent colors, the light shines through them, and no light can come upon the screen except that which passes through the figure, as is here represented.
There is no sheet to receive the picture, but the representation is thrown on a thin screen of silk or muslin placed betweenthe spectators and the lantern. The images are made to appear approaching and receding by removing the lantern further from the screen, or bringing it nearer to it. This is a great advantage over the arrangements of the magic lantern, and by it the most astonishing effects are often produced.
DISSOLVING VIEWS.
The dissolving views, by which one landscape or scene appears to pass into the other while the scene is changing, are produced by using two magic lanterns placed side by side, and that can be a little inclined towards each other when necessary, so as to mix the rays of light proceeding from the lenses of each together, which produces that confusion of images, in which one view melts as it were into the other, which gradually becomes clear and distinct.
HOW TO RAISE A GHOST.
The magic lantern or phantasmagoria, may be used in a number of marvelous ways, but in none more striking than in raising an apparent specter. Let an open box,A B, about three feet long, a foot and half broad, and two feet high, be prepared. At one end of this place a small swing dressing glass, and at the other let a magic lantern be fixed with its lenses in a direction towards the glass. A glass should now be made to slide up and down in the grooveC D, to which a cord and pulley should be attached, the end of the cord coming to the part of the box markedA. On this glass the most hideous specter that can be imagined may be painted, but in a squat or contracted position, and when all is done, the lid of the box must be prepared by raising a kind of gable at the end of the boxB, and in its lower part atE, an oval hole should be cut sufficiently large to suffer the rays reflected from the glass to pass through them. On the top of the boxFplace a chafing dish, upon which put some burning charcoal. Now light the lampGin the lantern,sprinklesome powdered camphor or white incense on the charcoal, adjust the slide on which the specter is painted, and the image will be thrown upon the smoke. In performing this featthe room must be darkened, and the box should be placed on a high table, that the hole through which the light comes may not be noticed.
THE THAUMATROPE.
This word is derived from two Greek words, one of which signifieswonder, and the otherto turn. It is a very pretty philosophical toy, and is founded upon the principle in optics, that an impression made upon the retina of the eye lasts for a short interval after the object which produced it has been withdrawn. The impression which the mind receives lasts for about the eighth part of a second, as may be easily shown by whirling round a lighted stick, which if made to complete the circle within that period, will exhibit not a fiery point, but a fiery circle in the air.
THE BIRD IN THE CAGE.
Cut a piece of cardboard of the size of a penny piece, and paint on one side a bird, and on the other a cage; fasten two pieces of thread, one on each side, at opposite points of the card, so that the card can be made to revolve by twirling the threads with the finger and thumb; while the toy is in its revolution, the bird will be seen within the cage. A bat may in the same manner be painted on one side of the card, and a cricketer upon the other, which will exhibit the same phenomenon, arising from the same principle.
CONSTRUCTION OF THE PHANTASMASCOPE.
The above-named figure is a Thaumatrope, as much as the one we are about to describe, although the term Phantasmascope is generally applied to the latter instrument; which consists of a disc of darkened tin-plate, with a slit or narrow opening in it, about two inches in length. It is fixed upon a stand, and the slit placed upwards, so that it may easily be looked through. Another disc of pasteboard, about a foot in diameter, is now prepared and fixed on a similar stand, but with this difference, that it is made to revolveround an axis in the center. On this pasteboard disc, paint in colors a number of frogs in relative and progressive positions of leaping; make between each figure a slit of about a quarter of an inch deep; and when this second disc is made to revolve at a foot distance behind the first, and the eye is placed near the slit, the whole of the figures, instead of appearing to revolve with the disc, will all appear in the attitudes of leaping up and down, increasing in agility as the velocity of the motion is increased. It is necessary, when trying the effect of this instrument, to stand before a looking-glass, and to present the painted face of the machine towards the glass.
A very great number of figures may be prepared toproducesimilar effects—horses with riders in various attitudes of leaping, toads crawling, snakes twisting and writhing, faces laughing and crying, men dancing, jugglers throwing up balls, &c.; all of which, by the peculiar arrangement above detailed, will seem to be in motion. A little ingenuity displayed in the construction and painting of the figures upon the pasteboard disc will afford a great fund of amusement.
CURIOUS OPTICAL ILLUSION.
One of the most curious facts relating to the science of vision is the absolute insensibility of a certain portion of the retina to the impression of light, so that the image of any object falling on that point would be invisible. When we look with the right eye, this point will be about fifteen degrees to the right of the object observed, or to the right of the axis of the eye, or the point of most distinct vision. When looking with the left eye, the point will be as far to the left. The point in question is the basis of the optic nerve, and its insensibility to light was first observed by the French philosopher, Mariotte. This remarkable phenomenon may be experimentally proved in the following manner:
Place on a sheet of writing-paper, at the distance of about three inches apart, two colored wafers; then, on looking at the left-hand wafer with the right eye, at the distance of about a foot, keeping the eye straight above the wafer, and both eyes parallel with the line which forms the wafers, the left eye being closed, the right-hand wafer will become invisible; and a similar effect will take place if we close the right eye, and look with the left.
ANOTHER.
Cut a circular piece of white paper, about two inches in diameter, which affix to a dark wall. At the distance of two feet on each side, but a little lower, make two marks; then place yourself directly opposite the paper, and hold the end of your finger before your face, so that when the right eye is open it shall conceal the mark on your left, and when the left eye is open the mark on your right. If you then look with both eyes at the end of your finger, the paper disc will be invisible.
ANOTHER.
Fix a similar disc of paper, two inches in diameter, at the height of your eye on a dark wall; a little lower than this, at the distance of two feet on the right hand, fix another of about three inches in diameter; now place yourself opposite the first sheet of paper, and, shutting the left eye, keep the right eye still fixed on the first object, and when at the distance of about ten feet, the second piece of paper will be invisible.
Or, fix three pieces of paper against the wall of a room, at equal distances, at the height of the eye. Place yourself directly before them, at a few yards distance, close your right eye, and look at them with your left, when you will see only two of them, suppose the first and second; alter your position a second time, and you will see the second and third, but never the whole three pieces together.
On a sheet of black paper, or other dark ground, place two white wafers, having their centers three inches distant. Vertically above the paper, and to the left, look with the right eye, at twelve inches from it, and so, that when looking down on it, the line joining the two eyes shall be parallel to that joining the center of the wafers. In this situation close the left eye, and look full with the right perpendicularly at the wafer below it, when this wafer only will be seen, the other being completely invisible. But if it be removed ever so little from its place, either to the right or left, above or below, it will become immediately visible, and start, as it were, into existence. "It will cease to be thought singular," says Sir John Herschel, "that this fact of the absolute invisibility of objects in a certain point of the field of view of each eye should be one of which not one person in ten thousand is apprized, when we learn that it is not extremelyuncommon to find persons who have for some time been totally blind with one eye without being aware of the fact."
THE PICTURE IN THE AIR.
One of the numerous optical illusions which have, from time to time, been evolved by scientific minds, is that of making an image or picture appear in the air. This is produced by means of a mirror, and an object in relief, upon which a strong light is thrown—the mirror being set at such an angle as to throw up the reflection of the image to a certain point, in the view of the spectator. This illusion is produced as follows: Let a screen be constructed in which is an arched aperture, the center of which may be five feet from the floor; behind the screen is placed a large mirror of an elliptical form. An object is now placed behind the screen, upon which the light of a strong lamp is thrown from a point above the mirror, and is received by the mirror and reflected to the center of the arched cavity in the screen, where it will appear to the spectator. Care should be taken to place the image in an inverted position, and the light should be so placed that none of it may reach the opening: the light must also be very powerful.
BREATHING LIGHT AND DARKNESS.
The following experiment, if performed with care, is exceedingly striking. LetSbe a candle, whose light falls at an angle of 56° 45´ upon two plate glasses,AB, placed close to each other; and let the reflected rays,A C,B D, fall at the same angle upon two similar plates,C D, but so placed that the plane of reflection from the latter is at right angles to the plane of reflection from the former. An eye placed atE, and looking at the same time on the two plates,CandD, will see very faint images of the candleS; which by a slight adjustment of the plates, may be made to disappear almost wholly, allowing the plateCto remain where it is. Change the position ofDtill its inclination to the rayB Dis diminished about 3°, or made nearly 53° 11´. The distance may be easily found by a little practice. When this is done, the image that had disappeared on looking intoD, will be restored, so that the spectator atE, upon looking into the two mirrors,CD, willsee no light inC, because the candle has nearly disappeared, while the candle is distinctly seen inD. If, while the spectator is looking into these two mirrors, either he or another person breathes upon them gently and quickly, the breath will revive the extinguished image inC, and will extinguish the visible image inD.
Explanation.—The lightA,C,B,Dis polarized by reflection from the platesAB, because it is incident at the polarizing angle 56° 45´ for glass. When we breathe upon the platesCD, we form upon their surface a thin film of water, whose polarizing angle is 53° 11´, so that if the polarized raysA C,B D, fall upon the platesC D, at an angle of 53° 11´, the candle from which they proceed would not be visible, or they would not suffer reflection from the platesC D. At all the other angles the light would be reflected, and the candle visible. Now the plateDis placed at an angle of 53° 11´, andCat an angle of 56° 45´, so that when a film of water is breathed upon them, the light will be reflected from the latter, and none from the former; that is, the act of breathing upon the glass plates will restore the invisible, and extinguish the visible image.
TO SHOW WHAT RAYS OF LIGHT DO NOT OBSTRUCT EACH OTHER.
Make a small hole in a sheet of pasteboardA, and placing it upright before three candlesB, placed closely together, it will be found that the images of all the candle flames will be formed separately on a piece of paperC, laid on the table to receive them. This proves that the rays of light do not obstruct each other in their progress, although all cross in passing through the hole.
HOW TO SEE THROUGH A PHILADELPHIA BRICK.
Construct a hollow box or case, like the figure in the margin. One side is purposely removed in the engraving, to enable you to see the arrangement of the interior,A,B,C, andD, are four small pieces of looking-glass, all placed at an angle of 45°, with respect to those sides of the box on which they are fixed; atEandG, two flat pieces of glass are inserted, as in the eye-glass of a telescope. Supposing you look through the openingE, in the direction of anobject placed atO, you would see it in the same manner as if there was an uninterrupted view betweenEandG, which is evidently not the case. The cause of this is readily explained. The image of the object atOis received on the looking-glassA, by which it is reflected toB, as it is again fromBtoC, and afterwards toD; and this last image inDis seen by the eye of the spectator placed atE, in the same direction as if in reality he was looking at the real object itself, in the direction of the dotted line fromOtoE. From this it is evident that the placing an opaque body atF, cannot prevent the object atObeing seen. Of course all this arrangement of the instrument is concealed, and you place it in the hands of a companion, that he may look throughEorG, it matters not which, at any object placed beyond. You may then safely lay a wager that your instrument is of so magical a nature that it will enable you to see through a brick wall; but as a single brick will be more convenient, and equally wonderful, you are willing to satisfy his doubts at once. Of course, the hand or the hat, or any other opaque object, will answer the same purpose.
THE STEREOSCOPE.
This is one of the newest and most interesting optical surprises invented, but, like many other instruments, it is indulged with a very hard name, which means, "Solids I see." For mere amusement, the instrument supplied with the necessary pictures may suffice, and they are now sold like the kaleidoscope at all optical instrument makers, toyshops, &c. The effect consists in obtaining the perfect solidity of a geometric object from two ordinary drawings, pictures of columns, statuary, figures, flowers, &c., &c., having a rounded appearance, "breadth," and keeping, which induce the spectator to believe he is gazing at the natural figure. Our limits preclude a lengthened description of thephilosophy of this instrument, the invention of Professor Wheatstone. We may, however, first recommend our readers to study the structure of the eye, in Brewster's Treatise on Optics, which may be thoroughly impressed on the mind by dissecting carefully the eye of a sheep or bullock. Now, if we cut open a portion of the eye of a recently killed animal, and look in upon the retina, which is a delicate network of nerves, and is considered the "mind of the eye," we shall behold all images inverted. How then, do we see them upright? Again, as we have two eyes at a distance from each other, the images formed on the two retinæ cannot be precisely alike: how is it that confusion is not the result, instead of perfect images, in which we can appreciate the geometric niceties of length, breadth, and thickness? Now the stereoscope assists us in understanding these difficult questions; and, quoting Professor Wheatstone, we find he states "that the theory which has obtained the greatest currency is that which assumes that an object is seen single because its pictures fall on corresponding points of the two retinæ; that is, on points which are similarly situated with respect to the two centers, both in distance and position. This theory supposes that the pictures projected on the retinæ, are exactly similar to each other corresponding points of the two pictures falling on corresponding points of the two retinæ."
Now, the fact is, that an object presents an entirely different appearance to each eye. Sir D. Brewster remarks, "That were a painter called upon to take drawings of a statue, as seen by each eye, he would fix at the height of his eyes a metallic plate, with two small holes in it, and he would then draw the statue as seen through the holes by each eye." With the utmost care, however, he could not reproduce the statue by their union. In order to do this, a camera withtwo lensesof the same aperture and focal length, placed at the same distance as thetwo eyes, must be constructed and used.
The stereoscope is, consequently, an imitation of the powers of the eyes, giving solidity and a perfect relievo appearance to any two pictures which might be drawn separately from the two lenses in the camera obscura mentioned. That is to say, if it were possible to be behind the retina of each eye, and draw the two pictures of any object seen by our eyes, those pictures put into the stereoscope,would reproduce the solidity from which they were drawn.
Two instruments are sold, and may be obtained with the photographic pictures, almost at any optician's, viz.: the reflecting and the refracting stereoscope, of which we give drawings.
THE REFLECTING STEREOSCOPE.REFRACTINGSTEREOSCOPE.
THE REFLECTING STEREOSCOPE.REFRACTINGSTEREOSCOPE.
THE REFLECTING STEREOSCOPE.REFRACTINGSTEREOSCOPE.
aa, the two pictures,BB, the two mirrors, so adjusted that their backs form an angle of ninety degrees with each other, i. e., the quarter of a circle.
OCULAR SPECTRA.
One of the most curious affections of the eye is that in virtue of which it sees what are calledocular spectra, or accidental colors. If we place a red wafer on a sheet of white paper, and, closing one eye, keep the other directed for some time to the center of the wafer, then, if we turn the same eye to another part of the paper, we shall see a green wafer, the color of which will continue to grow fainter and fainter, as we continue to look at it.
By using differently-colored wafers, we obtain the following results:
WAFER.SPECIMEN.Black,White.White,Black.Red,Bluish Green.Orange,Blue.Yellow,Indigo.Green,Violet, with a little Red.Blue,Orange Red.Indigo,Orange Yellow.Violet,Bluish Green.
BRILLIANT WATER MIRROR.
Nearly fill a glass tumbler with water, and hold it, with your back to the window, above the level of the eye, as in the engraving. Then look obliquely, as in the direction E,a,c, and you will see the whole surface shining like burnished silver, with a strong metallic reflection; and any object, as a spoon, A, C, B, immersed in the water, will have its immersed part, C B, reflected on the surface, as in a mirror, but with a brilliancy far surpassing that which can be obtained from quicksilver, or from the most highly-polished metals, by any means whatever.
OPTICS OF A SOAP BUBBLE.
If a soap-bubble be blown up, and set under a glass, so that the motion of air may not affect it, as the water glides down the sides and the top grows thinner, several colors will successively appear at the top, and spread themselves from thence down the sides of the bubble, till they vanish in the same order in which they appear. At length, a black spot appears at the top, and spreads till the bubble bursts.[7]
THE KALEIDOSCOPE.
If any object be placed between two plane mirrors, inclined towards each other at an angle of thirty degrees, three several images will be perceived in the circumference of a circle. On this principle is formed the kaleidoscope, invented by Sir David Brewster, and by means of which the reflected images viewed from a particular point exhibit symmetrical figures, under an infinite arrangement of beautiful forms and colors. The kaleidoscope may be bought at any toy-shop, but it is requisite that every young person should be able to construct one for himself. He must, therefore, procure a tube of tin or paper, of about teninches in length, and two and a half or three inches in diameter. One end of this should be stopped up with tin or paper, securely fastened, in which is to be made a hole, about the size of a small pea, for the eye to look through. Two pieces of well-silvered looking-glass,BB, are now to be procured; they must be not quite so long as the tube, and they should be placed in the tube lengthwise, at an angle of 60 degrees, meeting together in a point atA, and separating to the pointsCC, the polished surfaces looking inwards. A circular piece of glass is now to be laid on the top of the edges of the reflectors,BB; which, by their not being quite so long as the tube, will allow room for its falling in, and it will be supported by the edges of the tube, which may be slightly bent over, to prevent the glass from falling out. This having been done, now proceed to make the "cap" of the instrument. A rim of tin or pasteboard must be cut, so as to fit over the glass end of the tube; and in this, on the outer side, a piece of ground glass must be fastened, so that the whole may fit on the tube like the lid of a pill-box. Then, before putting it on, obtain some small pieces of broken glass of various colors, beads, little strips of wire, or any other object, and place them in the cap; and by passing it over the end, so that the broken glass, &c. has free motion, the instrument is complete. To use it, apply the eye to the small hole, and, on turning it, the most beautiful forms will appear, in the most wonderful combinations.
The following curious calculation has been made of the number of changes this instrument will admit of. Supposing it to contain 20 small pieces of glass, and that you make 10 changes in a minute, it will take an inconceivable space of time,i. e.462,880,899,576 years, and 360 days, to go through the immense number of changes of which it is capable.
SIMPLE SOLAR MICROSCOPE.
Having made a circular hole in a window-shutter, about three inches in diameter, place in it a glass lens of about twelve inches focal distance. To the inside of the hole adapt a tube, having at a small distance from the lens a slit, capable of receiving one or two very thin plates of glass, to which the object to be viewed must be affixed bymeans of a little gum water exceedingly transparent. Into this tube fit another, furnished at its extremity with a lens of half an inch focal distance. Place a mirror before the hole of the window-shutter on the outside, in such a manner as to throw the light of the sun into the tube, and you will have a solar magic lantern.
The method of employing this arrangement of lenses for microscopic purposes is as follows: Having darkened the room, and by means of the mirror reflected the sun's rays on the glasses in a direction parallel to the axis, place some small object between the two moveable plates of glass, or affix it to one of them with very transparent gum water, and bring it exactly into the axis of the tube; if the moveable tube be then pushed out or drawn in, till the object be a little beyond the focus, it will be seen painted very distinctly on a card, or piece of white paper, held at a proper distance, and will appear to be greatly magnified. A small insect will appear as a large animal, a hair as big as a walking-stick, and the almost invisible eels in paste or vinegar as large as common eels.
ANAMORPHOSES.
This is a very curious optical effect, producing a distorted and grotesque figure from a regular one. The term is derived from two Greek words, signifying a distortion of figure, and by its means many optical puzzles may be produced geometrically.
Take any subject, such as the portrait of a head; divide it vertically and horizontally with parallel lines, of which the outer sides shall form the boundary,A,B,C,D, and the whole shall be equi-distant. Then, on a separate piece of paper, or cardboard, prepare a drawing similar to Fig. 2 by the following means:
1. Draw a horizontal line,a b, equal toA B, and divide it into as many equal parts as the latter is divided.
2. Let fall a perpendicular line,e v, from the middle ofa b, and then draws vparallel toa b.
3. Bothe vands vmay be any length at pleasure, but the longer the first is, and the shorter the other, so will the anamorphoses be more and more deformed. The proportions in our figures are sufficiently different.
4. After having drawn from the pointvright lines,v1,v2,v3,v4, to the divisions ofa b, draw the lines b, andthrough each point wheres bintersects the divergent lines, draw other horizontal lines parallel toa b. We now have atrapezium,a b c d, divided into as many cells as the square in Fig. 1.
The next step is to fill up all the cells of Fig. 2 with portions of the device, proportionate to their position in Fig. 1. For instance, in Fig. 1 the nose is in the second vertical division from the left, and in the third and fourth horizontal divisions from the top, and that portion of the face must accordingly be placed in a corresponding part of Fig. 2.
By these means we procure the anamorphosis seen in Fig. 2, which, when viewed from a particular position, will lose all its distortion, and assume an appearance resembling that in Fig. 1. This position lies immediately over the pointv, and at a height above it equal to the length of the lines v; and the means of determining it are as follow:
Place the drawing horizontally before a window; take a slip of card, and rest its lower edge on the lines v, the card being accurately vertical; pierce a small hole in the card vertically over the pointv, and at a height from it equal to the length of the lines v, then, with the eye placed immediately behind the card, look through the orifice at the anamorphosis, and it will be found that as soon as the eye has become accustomed to the novelty of the experiment the anamorphosis will lose its distortion, and appear almost exactly like the symmetrical figure.
It would be very difficult, and would require geometrical reasoning of a lengthened kind, to show why this particular form of construction should lead to such results.
THE COSMORAMA.
The principle upon which the cosmorama is formed is so simple, that any person may easily fit up one in a small summer house, &c. Nothing more is necessary than to fix in a hole a double convex lens of about three feet focus,A, and at rather less than this distance a picture,B, is to be hung. To absorb all the rays of light but those necessary for seeing the picture, a squared frame of wood blackened on the inside is placed between the lens and the picture. The picture may be hung in a large box having a light coming in upon it from above, or in a small closet illuminated in the same manner. Should it be wished to show the picture by candle-light, a lamp,c, may be placed on the top of the wooden frame, and if the light of this be converged by a lens to a moderate radius, it will be more effective.
DISTORTED LANDSCAPES.
Landscapes or other matters may be drawn so as to produce curious optical illusions by the following method. Take a piece of smooth white pasteboard, and sketch the design upon it. Prick the outlines in every part with a fine pin or needle, then place the pricked drawing in a perpendicular position, and put a lighted candle behind it. Place before it another piece of pasteboard, and follow with a pencil the lines given by the light, and you have produced a distorted landscape. Now take away the candle and the pricked drawing, and place your eye where the light was, and the drawing will assume the regular form. To get your eye in the proper position, it will be advisable to cut out a piece of card according to the preceding pattern, and raising it on its base,B, look through the hole atA, when the object will appear in its proper proportions.
THE MAGIC COIN.
Among the numerous experiments with which science astonishes and sometimes even strikes terror into the ignorant, there is none more calculated to produce this effect than that of displaying to the eye in absolute darkness the legend or inscription upon a coin. To do this, take a silver coin (I have always used an old one), and after polishing the surface as much as possible, make the parts of it which are raised rough by the action of an acid, the parts not raised, or those which are to be rendered darkest, retaining their polish. If the coin thus prepared is placed upon a mass of red-hot iron, and removed into a dark room, the inscription upon it will become less luminous than the rest, so that it may be distinctly read by the spectator. The mass of red-hot iron should be concealed from the observer's eye, both for the purpose of rendering the eye fitter for observing the effect, and of removing all doubt that the inscription is really read in the dark, that is, without receiving any light, direct or reflected, from any other body. If, in place of polishing the depressed parts, and roughening its raised parts, we make the raised parts polished, and roughen the depressed parts, the inscription will now be less luminous than the depressed parts.
"These are machinations comical."—FORD.
"These are machinations comical."—FORD.
"These are machinations comical."—FORD.
There is no subject of such importance as Mechanics, as its principles are founded upon the properties of matter and the laws of motion; and in knowing something of these, the tyro will lay the foundation of all substantial knowledge.
The properties of matter are the following: Solidity (or Impenetrability), Divisibility, Mobility, Elasticity, Brittleness, Malleability, Ductility, and Tenacity.
The laws of motion are as follow:
1. Every body continues in a state of rest or of uniform rectilineal motion, unless affected by some extraneous force.
2. The change of motion is always proportionate to the impelling force.
3. Action and reaction are always equal and contrary.
EXPERIMENT OF THE LAW OF MOTION.
In shooting at "taw," if the marble be struck "plump," as it is called, it moves forward exactly in the same line of direction; but if struck sideways, it will move in an oblique direction, and its course will be in a line situated betweenthe direction of its former motion and that of the force impressed. This is called the resolution of forces.
BALANCING.
The center of gravity in a body is that part about which all the other parts equally balance each other. In balancing a stick upon the finger, or upon the chin, it is necessary only to keep the chin or finger exactly under the point which is called the center of gravity.
THE PRANCING HORSE.
Cut out the figure of a horse, and having fixed a curved iron wire to the under part of its body, place a small ball of lead upon it. Place the hind legs of the horse on the table, and it will rock to and fro. If the ball be removed, the horse would immediately tumble, because unsupported, the center of gravity being in the front of the prop; but upon the ball being replaced, the center of gravity immediately changes its position, and is brought under the prop, and the horse is again in equilibrio.
TO CONSTRUCT A FIGURE, WHICH, BEING PLACED UPON A CURVED SURFACE, AND INCLINED IN ANY POSITION, SHALL, WHEN LEFT TO ITSELF, RETURN TO ITS FORMER POSITION.
TO CONSTRUCT A FIGURE, WHICH, BEING PLACED UPON A CURVED SURFACE, AND INCLINED IN ANY POSITION, SHALL, WHEN LEFT TO ITSELF, RETURN TO ITS FORMER POSITION.
The feet of the figure rest on a curved pivot, which is sustained by two loaded balls below; for the weight of these balls being much greater than that of the figure, their effect is to bring the center of gravity of the whole beneath the point on which it rests; consequently the equilibrium will resist any slight force to disturb it.
TO MAKE A CARRIAGE RUN IN AN INVERTED POSITION WITHOUT FALLING.
It is pretty well known to most boys, that if a tumbler of water be placed within a broad wooden hoop, the whole may be whirled round without falling, owing to the centrifugal force. On the same principle, if a small carriage be placed on an iron band or rail, it will ascend the curve, become inverted, and descend again, without falling.
TO CAUSE A CYLINDER TO ROLL BY ITS OWN WEIGHT UP HILL.
Procure a coffee canister, and loading it atFwith a piece of lead, which may be fixed in with solder, the position of the center of gravity is thus altered. If a cylinder so constructed be placed on an inclined plane, and the loaded part above, it will roll up hill without assistance.
THE BALANCED STICK.
Procure a piece of wood, about nine inches in length and about half an inch in thickness, and thrust into its upper end the blades of two penknives, on either side one. Place the other end upon the tip of the fore-finger, and it will keep its place without falling.
THE CHINESE MANDARIN.
Construct out of the pith of elder a little mandarin; then provide a base for it to sit in, like a kettle-drum. Into this put some heavy substance, such as half a leaden bullet; fasten the figure to this, and in whatever position it may be placed, it will, when left to itself, immediately return to its upright position.
TO MAKE A QUARTER DOLLAR TURN ON ITS EDGE ON THE POINT OF A NEEDLE.
Take a bottle, with a cork in its neck, and in it, in a perpendicularposition, a middle-sized needle. Fix a quarter dollar into another cork, by cutting a nick in it; and stick into the same cork two small table-forks, opposite each other, with the handles inclining downwards. If the rim of the quarter dollar be now poised on the point of the needle, it may easily be made to spin round without falling, as the center of gravity is below the the center of suspension.
THE SELF-BALANCED PAIL.
You lay a stick across the table, letting one third of it project over the edge; and you undertake to hang a pail of water on it, without either fastening the stick on the table, or letting the pail rest on any support; and this feat the laws of gravitation will enable you literally to accomplish.
You take the pail of water, and hang it by the handle upon the projecting end of the stick, in such a manner that the handle may rest on it in an inclined position, with the middle of the pail within the edge of the table. That it may be fixed in this situation, place another stick with one of its ends resting against the side at the bottom of the pail, and its other end against the first stick, where there should be a notch to retain it. By these means, the pail will remain fixed in that situation, without being able to incline to either side; nor can the stick slide along the table, or move along its edge, without raising the center of gravity of the pail, and the water it contains.
TO LIFT A BOTTLE WITH A STRAW.