ATMOSPHERIC ELECTRICITY. 343 



blcmatical diurnal course, or in the explosion of the lightning 

 and thunder of the tempest, appears to stand in a manifold 

 relation to all phenomena of the distribution of heat, of the 

 pressure of the atmosphere and its disturbances, of hydro- 

 meteoric exhibitions, and probably also of the magnetism of 

 the external crust of the earth. It exercises a powerful 

 influence on the whole animal and vegetable world; not 

 merely by meteorological processes, as precipitations of 

 aqueous vapour, and of the acids and ammoniacal compounds to 

 which it gives rise, but also directly as an electric force acting 

 on the nerves, and promoting the circulation of the organic 

 juices. This is not a place in which to renew the discussion 

 that has been started regarding the actual source of atmo- 

 spheric electricity when the sky is clear, a phenomenon that has 

 alternately been ascribed to the evaporation of impure fluids 

 impregnated with earths and salts,* to the growth of plants,! 

 or to some other chemical decompositions on the surface of the 

 earth, to the unequal distribution of heat in the strata of the 

 air,J and, finally, according to Peltier's intelligent researches, 

 to the agency of a constant charge of negative electricity in 

 the terrestrial globe. Limiting itself to results yielded by 

 electrometric observations, such for instance as are furnished 

 by the ingenious electro-magnetic apparatus first proposed by 

 Colladon, the physical description of the universe should 

 merely notice the incontestible increase of intensity in the 

 general positive electricity of the atmosphere, || accompanying 

 an increase of altitude and the absence of trees, its daily varia- 

 tions (which, according to Clark's experiments at Dublin, 

 take place at more complicated periods than those found by 

 Saussure and myself), and its variations in the different seasons 

 of the year, at different distances from the equator, and in 

 the different relations of continental or oceanic surface. 



The electric equilibrium is less frequently disturbed where 



* Regarding the conditions of electricity from evaporation at high 

 temperatures, see Peltier, in the Annales de Chimie, t. Ixxv. p. 330. 



t Pouillet, in the Annales de Chimie, t. xxxv. p. 405. 



J De la Rive, in his admirable Essai historique sur VElectricite 

 p. 140. 



Peltier, in the Comptes rendus de TAcad. des Sciences, t xii. 

 p. 307 ; Becquerel, Traite de VElectricite et du Magnetisme, t. iv. 

 p. 107. 



II Duprez, Sur Vfflectritite de I Air, (Bruxelles, 1844,) pp. 56-61. 



