ATMOSPHERIC ELECTHICITY. 349 



tiical tension existing in the clouds the cause of the different forms 

 which these bodies assume. "At first," remarks he, "every vesicle pre- 

 serves an electric atmosphere like an independent and insulated body ; 

 then if all the reactions which follow have been in every respect equal, 

 the vapor should be uniformly diffused ; but it is sufficient that there 

 are inequalities in the density of the vapor, in order that there should 

 be inequality in the electrical reactions. The more powerful tensions 

 distributed in the different points react by repulsion on the internal 

 vapor ; they condense it, limit it more decidedly, and iorm the first 

 cloudy flakes. These, acting together as elementary vesicles, form by 

 their unison masses more complex, called fleeces, separated by in- 

 tervening clear spaces with jagged edges. Each of these fleeces is sur- 

 rounded by its own electrical sphere, which reacts on the flakes and 

 passes them together as the sphere of flakes reacted on the elementary 

 vesicles. These fleeces, regarded as elements, produce in their turnsfrata 

 or clouds, properly so called, and then afterwards form the cumuli of 

 different orders." The formation of the cirri reveals also, according to 

 M. Peltier, another electrical cause, namely, the attractive action of 

 two masses of vapors or of two separate bodies possessing different 

 electricities. The vapors interposed and attracted in the longitu- 

 dinal direction are formed in a line, while their unequal density in 

 the vertical direction, permitting an unequal distribution of electri- 

 city, there result lateral repulsions producing, fibrous condensa- 

 tions of vapors which constitute the cirri. This last effect may be re- 

 })roduced experimentally by substituting for the vapor small pieces of 

 gold leaf placed between bodies charged with opposite electricities. 

 These pieces of gold leaf are formed into line between the two bodies 

 and constitute threadlike conductors. M. Peltier relates that he like- 

 wise reproduced a part of this phenomenon with clouds formed of 

 small soap bubbles. 



CHAPTER IV. 



OF ATMOSPHERIC ELECTRICITY DURING RAIN, SNOW, AND STORMS. 



§ 1. — Of atmospheric electricity during rain and snoiv. 



When a cloud resolves itself into rain, every drop of water conveys 

 to the electrometer its electric atmosphere, and this attains an elec- 

 tric tension which is sometimes very considerable. Observers are not 

 all agreed respecting the changes which the electricity of this instru- 

 ment indicates, during the fall of rain. Tlius, according to Volta,* the 

 positive electricity increases on the approach of the cloud, and decrease 

 atterwards with the fall of the first drops of water, becomes nothing, 

 and finally passes to a very strong negative state. This electricity 

 preserves its intensity during half or an entire hour ; but if the rain 

 continues a longer time it decreases and becomes very feeble ; only it 



*Lehrbucli der Mctcorologie von Kacmtz, torn, II, p 418. 



