Take a piece of pasteboard, about five inches square, roll it into a tube with one end just large enough to fit round the eye, and the other end rather smaller. Hold the tube between the thumb and finger of the right hand; put the large end close against the right eye, and with the left hand hold a book against the side of the tube. Be sure and keep both eyes open, and there will appear to be a hole through the book, and objects, seem as if through the hole instead of through the tube. The right eye sees through the tube, and the left eye sees the book, and the two appearances are so confounded together that they cannot be separated. The left hand can be held against the tube instead of a book, and the hole will seem to be as if through the hand.
THE BLIND SPOT IN THE EYE.
| L. | R. |
Look with both eyes on these two letters; then shut the right eye while you look at the R, and gradually bring the book near your face. There is a point where the L will disappear. Repeat with a change of the eye employed.
THE BEWITCHED PLAYING CARD.
The dioptrical paradox consists of a hard-wood base, A, B, C, D, about eight inches square, with a groove in which slides coloured prints or drawings. Connected with the base are a pillar (E), a horizontal bar (F), with a tube (G) directly over the centre of the base, and containing a peculiarly shaped glass.
Fig. 122.
Performance.—An ace of diamonds, when placed on the base, will be actually shown as an ace of clubs to anybody looking down through the glass, or one animal is seen as another; in fact, any shape is presented as something different.
Explanation.—The glass (G) is like the common multiplying glass, except that its sides are flat and diverge from its hexagonal base upwards to a point in the axis of the glass, like a pyramid, each facet being an isosceles triangle.