ATMOSPHERIC ELECTRICITY. 341 



tity in the cloud just formed as in the mass of the air hefore the 

 formation of the cloud. "If," saj'S he, "a cloud is formed while the 

 air is pure and transparent, and the electricity is thus disseminated 

 in all its mass, every vesicle being a good conductor, the electricty 

 will unite at its surface in a stratum extremely thin, and may 

 remain in this state, if it is weak and if the aqueous vesicles are not 

 near each other. We shall thus have a cloud which in this state 

 will not be stormy; its electricitj' will be the same as that of the mass 

 of air in whicli it is formed, but its tension will be increased by its less 

 diffusion and its concentration around the vesicles. The cloud must 

 then appear more strongly electrified than the transparent air, as ob- 

 servation demonstrates. If the cloud is very dense, and consequently 

 the vesicles whicli form it are much closer, it may be regarded as a con- 

 tinuous conductor; and according to the laws of electric distribution 

 the fluid will abandon the interior of the cloud for its surface^ on which 

 it will diffuse itself in equilibrium, and will be there retained by the 

 pressure of the surrounding air." 



M. Gay Lussac thinks that the electricity usually diffused in the 

 air and collected in (his manner is sufficient to render clouds power- 

 fully electrical. 



In this way of considering the formation of electric cluuds, M. Gay 

 Lussac makes no mention of the nature of the electricity which is 

 transferred to their surface when they are very dense ; it must be ne- 

 cessarily admitted that it is positive, since the atmosphere in clear 

 weather always possesses positive electricity. We might, indeed, thus 

 explain the formation of clouds charged with positive electricity ; but 

 how cou d we conceive the exihtence of clouds negatively electrified, 

 when the atmosphere in which they are formed contains only positive 

 electricity. M. Lame* thus explains this phenomenon, " The clouds 

 occupying different heights, and experience indicating that atmospheric 

 electricity observed in clear weather is greater at greater distances from 

 the surface of the earh, it is conceived that the higher clouds, charged 

 with a greater quantity of positive electricity than those below, may 

 act by induction on the latter, repelling their positive fluid, which 

 being dissipated more quickly in the air than the fluid attracted, 

 leaves the negative electricity free on the lower clouds." But if it is 

 we admit that electric clouds exercise on each other an action by induc- 

 tion, still it is not seen how the positive fluid repelled should dissipate 

 itself sooner in the air than the fluid attracted ; ought not the contrary 

 rather to take place on account of the less distance which separates the 

 upper cloud from the portion of the lower cloud where the negative 

 electricity attracted may be accumulated? 



M. Becquerelf proposed a new theory of the formation of electric 

 clouds, Avhich embraces at once positive, negative, and neutral clouds. 

 According to this philosopher, the vapor which is formed on the 

 surface of the globe in general carry with it, besides the positive 

 electricity which is peculiar to it, a portion greater or less of the 

 negative electricity which the earth habitually possesses. '* Hence," 



'- Cours de Physique de Ecole Polytechnique, toin II, 2d part, page SO. Paris, 1S37. 

 j Traite de I'Electricitc et du Magnctisme, torn IV, p. 121. 



