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

larized electricity which they severally contain. As these minute globular particles increase in density and extent, the tension of their free electricity becomes greater, until this speedily reaches such a degree as to overcome the resistance of the non-conduct- ing air, when a discharge of lightning takes place, either to the earth or to some other cloud less charged. Thunder clouds arc often negative in regard to each other, as also in regard to the earth; in that case the lightning is seen to leap from one to the other, until the equilibrium is nearly or quite restored between them. But it is the new and isolated thunder clouds, those which form so rapidly from vapor con- densed by the violent meeting of very warm and very cold cur- rents of air, that present the highest degree of electric excite- ment, and exhibit the most terrific electric phenomena. As the thunder storm and shower clouds now approach, the flaky portions of these clouds are observed to be in the greatest com- motion by a whirling and flying of various detached portions, and a scudding of other fragments to other denser portions, as if to find an adjustment—the whole having a dismal, dark, or black and threatening aspect, which are instantly and fearfully augmenting; and then comes the blazing of frequent discharges of lightning, followed by, or almost simultaneous with, crash- ing peals of terrific thunder, and that with torrents of rain. These thunder clouds, then, may be regarded as a huge pano- rama of electric batteries suspended in the sky and insulated merely by the surrounding air. Thus prodigious quantities of electricity are restored to the earth's surface again by the lightning and the falling snow or rain. But M. De la Rive believes that a still greater quantity of electricity from the higher regions of atmosphere returns to the earth at the magnetic poles. Thus the quantities of elec- tricity which pass into the air in all the equatorial and temperate regions, flow through the air in currents towards the north and south poles, and are there discharged into the earth at and about the magnetic axes ; and from thence flow through the earth back again towards the equator, for reestablishing the equilibrium. This philosopher believes that such a process accounts for the beautiful, but often pain-attending phenomena of the aurora bo-