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The Barometer: Recreation

An ingenious Recreation, called the Two Communicative Busts. Take two heads of plaster of Paris, and place them on pedestals on the opposite sides of a room. Then take a tin tube, of an inch in diameter, and let it pass from the ear of one head through the pedestal, and under the floor, to the mouth of the other, observing, that the end of the tube which is next the ear of one head, should be considerably larger than that which comes to the mouth of the other.

The whole being so disposed that there may be no suspicion of a communication, let any person speak with a low voice into the ear of one bust, and the sound will be distinctly heard by any one who shall place his ear to the mouth of the other; and if there be two tubes, one going to the ear, and the other to the mouth of each head, two persons may converse together, by applying their mouth and ear reciprocally to the mouth and ear of the busts, without being heard by any other persons in the room.

Another Recreation of the same kind, called the Oracular Head. Place a bust on a pedestal in the corner of a room, and let there be two tubes, one of which goes from the mouth, and the other from the ear of the bust, through the pedestal and floor, to an under apartment.

Then if a person be placed in the under room, by applying his ear to one of the tubes as soon as a proper signal is given, he will hear any question that is asked, and can immediately return an answer; and if wires be contrived to go from the under jaw and eyes of the bust, they may be made to move at the same time, and by these means appear to deliver the answer.

It was by a contrivance of this kind, that Don Antonio de Moreno so much astonished the celebrated Knight of the Woeful Countenance, and his facetious squire Sancho Panza, by resolving certain doubts proposed by the former concerning his adventures in the cave of Montesinos, and the disenchantment of my lady Dulcinea.

How to make a Piece of Metal, or any other heavy Body, swim upon the Surface of Water, like a Cork he specific gravity of water is inferior to tha of metals, and consequently water, absolutely speaking, cannot support a ball of iron or lead; but if this ball be flattened, and beat out to a very thin plate, it will, if put softly upon still water, be prevented from sinking, and will swim upon its surface like ary light substance. In like manner, if a fine steel needle. 1 APPENDIX which is perfectly dry, be placed gently upon some still water in a vessel, it will float upon the surface without sinking. But if you would have a metallic body of large dimensions to swim upon water, you must reduce it into a thin concave plate, like a kettle; in which case, as the air it contains, to-- gether with the body itself, weighs less than the same bulk of water, it cannot possibly sink; as is evident from large copper boats, or pontoons, by which whole armies have frequently passed over rivers without danger. If this concave metallic vessel be placed upon the water with its mouth downwards, it will swim as before, and the contained air will keep the bottom of it from being wet; for that the water will not rise into any hollow vessel which is immersed into it, may be made evident thus:-Take a glass tumbler, and plunge it into water with its mouth downwards, and you will find, when you take it out, that the inside of the vessel is perfectly dry, so that if a live coal were put there, it would not be extinguished.

A curious Experiment, to prove that Two and Two do not make Four.

Take a glass vessel with a long narrow neck, which, being filled with water, will hold exactly a quart; then put into this vessel a pint of water, and a pint of acid of vitriol, and you will presently perceive, that the mixture will not fill the vessel, as it did when a quart of water only was put into it. The acid of vitriol must be put in gradually, by little and little at a time, mixing each portion with the water before you add more, by shaking the bottle, and leaving its mouth open, otherwise the bottle will burst. The mixture in this case also possesses a considerable degree of heat, though the two ingredients of themselves are perfectly cold; and this phenomenon is not to be accounted for, by supposing that the acid of vitriol is received into the pores of the water, for then a small portion of it might be absorbed by the water, without augmenting its bulk, which is known not to be the case; but the very form of the bodies in this experiment is changed, there being, as Dr. Hooke, who first noticed the fact, observes, an actual penetration of dimensions. Chemistry also furnishes a number of other instances, which shew that two bodies, when mixed together, possess less space than when they are separate.

An ingenious Method of Secret Writing, by means of corresponding Spaces. Take two pieces of pasteboard, or stiff paper, out of which cut a number of oblong figures, at different distances from each other, as in the following example. Keep one of these pieces for yourself, and give one to your correspondent; and when you are desirous of sending him any secret intelligence, lay the pasteboard upon a sheet of paper of the same size, and in the spaces which are cut out, write what you would have him only to understand, and fill up the intermediate parts of the paper with something which makes with these words a different sense. Then, when your correspondent receives this letter, by applying it to his pasteboard, he will be able to comprehend your meaning.

EXAMPLE.

I shall be | much obliged to you, as reading | alone | engages my attention | at present, if you will send me any of the | eight | volumes of the Spectator; I hope you will excuse this freedom, but for a winter's | evening don't know a better entertainment. If I ☐ fail | to return it soon, never trust me for the time to come.

A curious Experiment, which depends on an Optical Illusion. I On the bottom of the vessel, (see Plate,) AIBD, fig. 6, place three pieces of money, as a half-crown, a shilling, and a sixpence; the first at E, the second at F, and the third at G. Then let a person be placed with his eye at H, so that he can see no farther into the vessel than I; and tell him, that by pouring water into the vessel, you will make him see three different pieces of money, which he may observe are not poured in with the water.

For this purpose, desire him to keep himself steady in the same position, and, pouring the water in gently, that the pieces of money may not be moved out of their places, when it comes up to K, the piece G will become visible to him; when it comes up to L, he will see the two pieces G and F; and when it rises to M, all the three pieces will become visible: the cause of which is owing to the refraction of the rays of light, in their passage through the water; for while the vessel is empty, the ray HI will proceed in a straight line; but in proportion as it is filled with water, the ray will be bent into the several directions NG, OF, PE, and by these means the pieces are rendered visible.