[14] Ganot: Eléments de Physique.
[15] Encly. Metrop.
[16] “Treatise on Electricity and Magnetism.”
[17] Sabine: “The Electric Telegraph.”
[18] We are indebted for many facts respecting Mr. Edison’s light in this chapter to a paper by Mr. Upton.
[19] It is the same with a number of other common products, such as clay, sandstone, etc., the composition of which chemistry has revealed. Argil, or clay, slate, and schist all contain a metal—aluminium, which has become most valuable for industrial purposes. Stones for building are composed of a metal combined with carbon and oxygen—calcium; sandstone is composed of silicium, a metallic body united with oxygen; and sulphate of magnesia, which enters into the composition of a purgative drink, also contains a metal—magnesium.
[20] These substances must be finely powdered and thoroughly mixed.
[21] Requires oxy-hydrogen blow-pipe.
[22] Cyanogen, ethyl, and cacodyl, are compound radicals.
[23] A crystal should be held so that one of its axes is vertical to the spectator. This axis is termed the principal axis, and when there is inequality the longest axis is the principal.