Part 18 (2/2)
[Ill.u.s.tration: Fig. 23.]
Place four persons in front of the four sides, and at equal distances from the box, and then draw them up that they may see themselves in the mirrors, when each of them, instead of his own figure, will see that of the person next to him, but who will appear to him to be placed on the opposite side. Their confusion will be the greater, as it will be very difficult, if not impossible, for them to discover the mirrors concealed in the box. The reason of this phenomenon is evident; for though the rays of light may be turned aside by a mirror, yet they always _appear_ to proceed in right lines.
_The Perspective Mirror._
Provide a box, A B C D, Fig. 24, of about two feet long, 15 inches wide, and 12 inches high. At the end A C, place the concave mirror, the focus of whose parallel rays is 18 inches from the reflecting surface. At I L place a pasteboard, blacked, in which a hole is cut, sufficiently large to see on the mirror H the object placed at B E F D. Cover the top of the box, from A to I, close, that the mirror H may be entirely darkened. The other part, I B, must be covered with gla.s.s, under which is placed a gauze, or oiled paper, to prevent the inside from being seen. Make an aperture at G, near the top of the side E B, beneath which, on the inside, place in succession, paintings of vistas, landscapes, figures, &c., so that they may be in front of the mirror H. Let the box be placed that the objects may be strongly illuminated by the sun, or by wax-lights placed under the enclosed part of the box A I. By this simple construction, the objects placed at G D will be thrown into their natural perspective, and if the subjects be properly chosen and well executed, the appearance will be both wonderful and pleasing.
[Ill.u.s.tration: Fig. 24.]
_Gunpowder Exploded by Reflection._
Place two concave mirrors at about 12 or 15 feet distance from each other, and let the axis of each be in the same line. In the focus of one of them place a live coal, and in the focus of the other place some gunpowder. With a pair of double bellows, which make a continual blast, keep constantly blowing the coal, and notwithstanding the distance between them, the powder will presently take fire.
_The Igniting Mirrors._
The rays of a luminous body placed in the focus of concave mirror, being reflected in parallel lines, and a second mirror being placed diametrically opposite to the first, will set fire to a combustible body, by collecting those rays in the focus.
_The Armed Apparition._
If a person with a drawn sword place himself before a large concave mirror, but further from it than its focus, he will see an inverted image of himself in the air, between him and the mirror, of a less size than himself. If he steadily present the sword towards the centre of the mirror, an image of the sword will come out from it, point to point, as if to fence with him; and by his pus.h.i.+ng the sword nearer, the image will appear to come nearer to him, and almost to touch his breast. If the mirror be turned 45 degrees, or one-eighth round, the reflected image will go out perpendicularly to the direction of the sword presented, and apparently come to another person placed in the direction of the motion of the image, who, if he be unacquainted with the experiment, and does not see the original sword, will be much surprised and alarmed.
_The Phantom._
You inform a person that at a certain hour, and in a certain place, he shall see the apparition of a deceased friend, (whose portrait you possess.) In order to produce this phantom, there must be a door which opens into an apartment to which there is a considerable descent.
Under that door you are to place the portrait, which must be inverted and strongly illuminated, that it may be brightly reflected by the mirror, which must be large and well polished. Then having introduced the incredulous spectator at another door, and placed him in the proper point of view, you suddenly throw open the door, when to his great surprise he will view the apparition of his friend.
_The Distorting Mirror._
Opticians sometimes grind a gla.s.s mirror concave in one direction only, or longitudinally; it is in fact a concave portion of a cylinder, the breadth of which may be considered that of the mirror. A person looking at his face in this mirror, in the direction of its concavity, will see it curiously distorted in a very lengthened appearance; and by turning the cylindrical mirror a quarter round, his visage will appear distorted another way, by an apparent increase in width only. If in a very near situation before it, you put your finger on the right hand side of your nose, it will appear the same in the mirror; but if in a distant situation, somewhat beyond the centre of concavity, you again look at your face in the mirror, your finger will appear to be removed to the other side of your nose.
_Water colder than Ice._
Put a lump of ice into an equal quant.i.ty of water, heated to 176 degrees, the result will be, that the fluid will be no hotter than water just beginning to freeze; but if a little sea salt be added to the water, and it be heated only to 166 or 170, a fluid will be produced _colder than the ice was at first_.
_Exploding Salt._
If a small quant.i.ty of powdered charcoal and hyper-oxymuriate of potash be rubbed together in a mortar, an explosion will be produced, and the charcoal inflamed. Three parts of this salt, and one of sulphur, rubbed together in a mortar, produce a violent detonation. If struck with a hammer on an anvil, there is an explosion like the report of a pistol.
When concentrated sulphuric acid is poured upon this salt, there is a considerable explosion; it is thrown about to a great distance, sometimes with a red flame; and there is exhaled a brown vapour, accompanied with a strong odour.
_Dioptrical Paradox._
Construct a machine similar to that in Fig. 25. Its effect will be, that a print, or an ornamented drawing, with any object, such as an ace of diamonds, &c. in the centre F, will be seen as an ace of clubs when placed in the machine, and viewed through a single plane gla.s.s only, contained in the tube E. The gla.s.s in the tube F, which produces this surprising change, is somewhat on the principle of the common multiplying gla.s.s, as represented at G, which, by the number of its inclined surfaces, and from the refractive power of the rays proceeding from the objects placed before it shows it in a multiplied state. The only difference is, that the sides of this gla.s.s are flat, and diverge upwards from the base to a point in the axis of the gla.s.s like a cone; it has six sides, and each side, from its angular position to the eye, has the property of refracting from the border of the print F, such a portion of it (designedly placed there) as will make a part in the composition of the figure to be represented; for the hexagonal and conical figure of this gla.s.s prevents any part of the ace of diamonds being seen; consequently the ace of clubs being previously and mechanically drawn in the circle of refraction in six different parts of the border, at 1, 2, 3, 4, 5, 6, and artfully disguised in the ornamental border, by blending them with it, the gla.s.s in the tube at E will change the appearance of the ace of diamonds, F, into the ace of clubs, G. In the same manner many other prints undergo similar changes, according to the will of an ingenious draughtsman who may design them. The figure of the gla.s.s is shown at H.
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