Electro-physiology and electro-therapeutics : showing the best methods for the medical uses of electricity / By Alfred C. Garratt.

Electric Relations of the Earth to its Atmosphere. Professor Faraday introduced and expounded, at a lecture before the Royal Institute, the hypothesis of M. Pelletier re- specting the electrical relations of the earth and its atmosphere to the " planetary space " in which it moves. The method by which the electricity of the atmosphere was determined by MM. Pelletier and Quitelet was shown to correspond very nearly with those of Bccquerel and De la Rive. The instrument employed by these investigators was a brass globe, placed on a thin metallic stem, to which is affixed a delicate galvanometer needle, which indicates by a minute measurement in degrees, the amount of electricity obtained.* This instrument was used on the summits of high buildings, where it was above every surrounding object. The method formerly adopted was to employ for this purpose a long metallic rod, furnished with points which projected into the air, to be examined. M. Pelletier's mode gives the quantity, and the kind, with great certainty ; while the old method furnishes un- certain and often contradictory results. Dr. Faraday illustrated, by enlarged models, the influence of various degrees of elevation on M. Pelletier's electrometer ; at the same time showing that no changes take place from variation of position, when the in- strument is moved horizontally, and that thus, throughout each stratum, the electricity of the air is the same. It is the vertical elevation, or depression, which produces a marked difference. The results obtained by M. Pelletier are, — 1. That the electricity of the air increases directly with the distance from the surface of the earth — a fact of great im- portance, as it influences the determination of the question whether the electricity of the earth be derived from planetary space, as Pelletier affirms, or whether, as Professor Faraday thinks, it be the result of various processes taking place on the surface of the earth. 2. The measure of divergence of the electrometer being * Med. Gazette, February, 1850, p. 255.