ATMOSPHERIC ELECTRICITY. 321 



dish dry fogs whicli are strongly negative ; they act at a less distance 

 and produce a greater inductive effect. These fogs show also what a 

 series of discharges would he produced between the gold leaves and 

 the armatures, if it were the air which was the electrified body." 



These experiments place beyond doubt the existence of the nega- 

 tive electricity of the earth, of which M. Peltier speaks. It had 

 previously attracted the attention of De Saussure,* who, by a particular 

 arrangement of his electrometer, sought to ascertain its variations. 

 The most direct means of determining it consists in placing one of the 

 ends of a platina wire of a rheometer in a moist part of the ground, 

 and the other in a dry portion of the same ground or under an ad- 

 joining building. This part of the ground or of the building being, 

 on account of its partial conductibility, less charged with' electricity 

 than the moist ground, the electrical equilibrium is established be- 

 tween the two by the means of the metallic wire, and results in 

 an action on the magnetic needle. In this way M. Peltier f ascer- 

 tained that duiing clear weather the ground is constantly negative at 

 very different tensions, according to the hygrometric state and tem- 

 perature of the air. But if it be true that the earth possesses a nega- 

 tive electricity, and that an electrometer placed under a clear sky 

 becomes electrified by induction, and not by contact of the surround- 

 ing air, must we conclude, with M. Peltier, that the air is wholly 

 deprived of electricity? This philosopher introduced the positive in- 

 duction of celestial space in the electrical phenomena of the atmos- 

 phere ; but he used this language only that he might be the more 

 easily understood. According to him, ponderable bodies only have 

 the power of controlling the cause of electric phenomena. Empty 

 space, therefore, can control nothing. The earth, as a ponderable 

 body, possesses the power of coercion which M. Peltier calls negative 

 electricity, while celestial space, not being able to control this cause, 

 owes to this negative quality an electric reaction, which he calls vitre- 

 ous electricity. Further, this philosopher admits neither the theory 

 of the two electric fluids nor that of one fluid; but he regards the cause 

 of electric phenomena, the same as that of light and heat, as a 

 modification of a universal fluid which fills all spac3, and the terms of 

 "vitreous" and "resinous" have for him no other meaning than that 

 of indicating the different degrees of one and the same state, beginning 

 at a point of equilibrium deprived of all electric manifestation. It is 

 by these considerations that he explains the phenomena which the 

 electroscopes present when they are raised or lowered. This interpre- 

 tation of atmospheric electricity is then joined to a new theory of 

 electricity, which M, Peltier has hitherto only indicated, and of which 

 he promises afterwards to furnish all the details. However this may be, 

 it appears that the different methods of managing electroscopes under 

 a clear sky could likewise be explained by the theory of two electric 

 fluids and by the hypothesis of different atmospheric strata progressively 

 electrified. We might, however, ask how it happens that an electro- 

 scope which has been brought to an equilibrium presents no diver- 



* Voyages dans lea Alpea, torn. II, § 830, page 254. 



■j- Traite de I'Electricite ct du Magnetism, par Bec(iuerel, torn. IV, p. 107. 



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