ATMOSPHERIC ELECTRICITY. dl5 



which are mingled with the steam, against the sides of the orifice 

 through which the steam escapes; neither dry steam nor dry air is 

 capable oi' exciting electricity by friction. This is in accordance with 

 the experiment ot De Saussure mentioned at page 296 of tliis article.] 



Atmospheric electricity being very weak before the formation of a 

 storm, and rapidly attaining its maximum in the thunder-cloud, Volta 

 concluded that the vapors which rise in the air have their electricity 

 latent and set it free on their condensation. But nothing appears to 

 authorize the admission that one of the electricities can be rendered 

 latent, without the presence of the contrary, and that the one can 

 exist insulated without the other ; for it is an undoubted principle 

 that, whenever electricity is produced, its positive and its negative states 

 exhibit themselves simultaneously with the same intensity. These 

 considerations appear to us sufficient to prove that Yolta's theory cannot 

 be admitted in the present state of science. 



The question as to the origin of atmospheric electricity has also been 

 the object of M. Pouillet's researches. This philosopher found, by 

 numerous experiments, that simple evaporation produced in a pla- 

 tina crucible, whether slowly or rapidly, never disengages electri- 

 city when it is not accompanied by chemical action ; but that it 

 always produces electricity when the water which is evaporated holds 

 in solution gases, acids, or salts. In this case the steam takes the 

 positive electricity, and the solution the negative. He observed the 

 same phenomena with solutions of alkalies ; but the steam then took 

 the negative electricity, and the alkali the positive.* Applying 

 these results to the evaporation which takes place constantly at the 

 surface of the earth, M. Pouillet remarked that the waters of the sea, 

 and, in geaeral, those which plants imbibe and those which moisten 

 the surface of the ground, always hold in solution foreign substan- 

 ces, which they leave behind; and hence at the surface of the earth 

 there is no evaporation M'ithout there being, at the same time, chem- 

 ical segregation, and consequently the production of electricity. He 

 also believed that it followed, from his experiments, that all the vapors 

 which form at the surface of the earth are brought into an electric 

 state, not by evaporation, as Volta supposes, but because the water, in 

 being evaporated, leaves the foreign substances which it held in solu- 

 tion. This may be, according to that philosopher, one of the causes 

 of the positive electricity which is observed in the air in clear weather. 



M. Peltier,! from similar experiments, arrived at a different conclu- 

 sion. He showed that, in the evaporation of saline solutions, we only 

 obtain signs of electricity in the case of a rapid segregation of the 

 dissolved body, produced by the action of the elevated temperature of 



*See the Journal L'Institut of October 21, 18-11, No. 403. 



tM. PouiUet made use of a platina crucible in order to remove the cruises which might 

 produce electro-chemical effects. This crucible, brought successively to various tempera- 

 tures, was placed on a disk, or metallic ring connected by a brass stem with the lower plate 

 of a gold-leaf condenser. See his Memoir, Annales de Cliimie et de Physique, torn. 

 XXXVI, p. 5. 1827. 



ijlConiptts Picndus, torn. II, p. 908, 1840 ; and Annales de Chimie et de Physique, torn. 

 LXXV, p. 330, 1840 It was with a needle electrometer, dcscril)ed in vol. LXII of the 

 Annales de Chimie et de Physique, that M. Peltier made his experiments. 



