Make two holes in the wainscot of a room, each a foot high and ten inches wide, and about a foot distant from each other. Let these apertures be about the height of a man's head, and in each of them place a transparent glass in a frame, like a common mirror.
Behind the partition, and directly facing each aperture, place two mirrors enclosed in the wainscot, in an angle of forty-five degrees.[B] These mirrors are each to be eighteen inches square: and all the space between them must be enclosed with pasteboard painted black, and well closed, that no light can enter; let there be also two curtains to cover them, which you may draw aside at pleasure.
When a person looks into one of these fictitious mirrors, instead of seeing his own face he will see the object that is in front of the other; thus, if two persons stand at the same time before these mirrors, instead of each seeing himself; they will reciprocally see each other.
There should be a sconce with a lighted candle, placed on each side of the two glasses in the wainscot, to enlighten the faces of the persons who look in them, or the experiment will not have so remarkable an effect.
[B] That is, half-way between a line drawn perpendicularly to the ground and its surface.
To cause a brilliant Explosion under Water.
Drop a piece of phosphorus, the size of a pea, into a tumbler of hot water; and, from a bladder furnished with a stop-cock, force a stream of oxygen directly upon it. This will afford a most brilliant combustion under water.
Fulminating Mercury.
Dissolve 100 grains of mercury by heat, in an ounce and a half of nitric acid. This solution being poured cold upon two measured ounces of alcohol previously introduced into any convenient glass vessel, a moderate heat is to be applied, till effervescence is excited. A white fume then begins to appear on the surface of the liquor, and the powder will be gradually precipitated when the action ceases. The precipitate is to be immediately collected on a filter, well washed with distilled water, and cautiously dried in a heat not exceeding that of a water-bath. Washing the powder immediately is material, because it is liable to the re-action of the nitric acid; and, while any of the acid adheres to it, it is very subject to the action of light. From 100 grains of mercury, about 130 of the powder are obtained.
This powder, when struck on an anvil with a hammer, explodes with a sharp stunning noise, and with such force as to indent both hammer and anvil. Three or four grains are sufficient for one experiment.