ATMOSPHERIC ELECTRICITY. 313 



Other philosophers have limited themselves to simple conjectures. 

 In a memoir containinc^ his observations on atmospheric electricity, 

 Canton* threw out in advance this question : Might not suddenly rari- 

 fied air impart electricity to clouds and vapors,, and would not condensed 

 air produce a similar effect? Priestleyf inquired if the empty space 

 which is above the clouds might not always have an electricity opposed 

 to that of the earth? May not thunder and earthquakes, he adds, be 

 owing to a re-establishment of the equilibrium between the two elec- 

 tricities ? 



According to Beccaria,;}: electricity proceeds from tlie earth wherever 

 the ground is surcharged, bearing with it the light bodies which may 

 facilitate its passage. These bodies thus assist in transferring to tlie 

 atmosphere the electricity of the earth. 



Franklin§ considered the sea as the source of lightning, founding his 

 opinion on the light which it exhibits at night on the slightest agita- 

 tion. In his view, the particles of water are so many little solid spheres, 

 which only touch the salt in some points, and he supposes there exists 

 between these particles and those of salt, the same friction there is 

 between the glass and the cusiiion of the electrical machine ; so that a 

 particle of water at the surface, being surrounded by an electric atmos- 

 phere, is repelled, and conveys to the air the electricity with which it 

 is charged. 



It was in the evaporation of water at the surface of the earth that 

 Volta|l sought for the cause of atmospheric electricity. According to 

 this celebrated scientist a body on being reduced to vapor acquires 

 a greater capacity for electricity as well as for caloric. In the case of 

 water, the vapor in forming absorbs positive electricity and renders 

 it latent, while the water becomes negatively electriiied. When this 

 vapor again condenses in the colder strata of air which it meets as it 

 it rises, its electricity is disengaged, and the feeble conductibility of the 

 air would prevent its return to the earth, from which it originated, if it 

 were not for rain, snow, hail, or violent discharges. This theory, 

 which was likewise adopted by Saussure,Tf is based, first, on the pro- 

 duction of electricity in the passage of a body from one state to 

 another. Second, on the preservation of the same quantity of electricity 

 in a latent state by the body as long as the molecules of the latter 

 continue in the same state of aggregation. Volta sought to verify by 

 experiment the first of the above suppositions. Placing in com- 

 munication with its condenser a metallic vase,** in which he caused 

 water to be evaporated, he obtained, in concert with Lavoisier and 



* Transactions I'hilosophiquos, tome XLVIII, Ist part, page 357, 1753. 



f Historie de Electricite, tome III, page 32. 



t Lettcre dell' Electricismo, page 2()2. 



§ Experim. and Observ. on Electricity, page 175. 



II Journal do Physique, tome XXIII, page 'Jti, 1783. 



i Voyages dans les Alpes, tomo II, sec. 829, page 252. 



^'■^ This experiment has been tiie subject of a ({uestion of priority between Volta on the one 

 side and La Place and Lavoisier on the other. See the historical eulogy on Volta by M. Arago, 

 Annales de Chemie et do Physique, vol. 44, page 396. Wo may observe that attempts 

 had already been previously made in England to ascertain whether evaporation contributes 

 to the production of electricity. We find in the 3dv(dume of the History of Electricity by 

 Priestley, page 440, that this philosopher placed a small quauuty of water on a small bit of 

 glass and made it evaporate rapidly by means of a red-hot iron which he held under it. He did 

 not notice that the glass acquired any sensible degree of electricity. 



