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 glass

only, contained in the tube E. The glass in the tube F, which produces

this surprising change, is somewhat on the principle of the common

multiplying glass, 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 glass are flat,

and diverge upwards from the base to a point in the axis of the glass

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 glass 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

glass 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 glass is shown at


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