314 ATMOSPHEEIC ELECTRICITY. 



La Place, manifest signs of negative electricity. But as these illus- 

 trious philosophers carried on their experiments in metallic vessels 

 which were aifected by water; the results at which they arrived could 

 not lead them to the truth, since they knew not that the slightest 

 chemical action produces electrical effects; they therefore attributed to 

 the change in the molecular state of bodies that which ought to have 

 been referred to the combination of the same bodies with other elements. 

 Hence resulted the frequent contradictions which De Saussure* obtained 

 in repeating this experiment. When he caused water to be evaporated 

 in an iron crucible his electrometer was electrified, sometimes posi- 

 tively, sometimes negatively, and sometimes even remained without 

 presenting any signs of electricity. 



Science possesses facts which philosphers have cited in support of the 

 opinion that there is a disengagement of electricity on the change of 

 state of bodies. Wilke observed that certain bodies, like sulphur, 

 wax, &c., poured into glass vases, where they were left to cool, exhibit 

 when they are withdrawn, strong negative electricity, while the glass 

 exhibits positive electricity of equal intensity. But if the change of 

 state were the true cause of this phenomenon, ought it not to produce 

 electricity in the solidifying of any body whatever ? Now this does 

 not take place. M. Gay Lussacf ascertained that the adhesion of bodies 

 and their separation by the inequality of their contraction, as is the case 

 of sulphur and glass, wax and glass, &c., are indispensable condition 

 for obtaining electricity after the fusion and solidifying of a body. The 

 electricity observed in this case must then be attributed to another cause 

 than the change of state, which appears to reside in the pressure which 

 the two bodies exert on each other. The electrical state of steam at the 

 moment it comes out of a boiler has been cited as favorable to Volta's 

 theory. I But, though the disengagement of electricity is in this case 

 unquestionable, still it is very difficult to attribute it to the evapora- 

 tion of the water, since it is only at the instant of the expansion of 

 the steam that the electricity is exhibited. Must we not rather refer 

 this phenomenon to the expansion, or to -some circumstance which 

 accompanies it, such as the diminution of the pressure of the steam 

 against the sides of the boiler ? This latter opinion is strengthened 

 by the fact that jets of atmospheric air act precisely in the same manner 

 as those of steam. If we compress air in a vessel, such as the recepta- 

 cle of a portable fountain, and then let it quickly pass off in a jet, 

 we observe that an electrometer which is exposed to the current of air 

 becomes positively electrified, while the vessel, if it be insulated, shows 

 signs of negative electricity. § Possibly it may be the same cause which 

 produces the electricity which M. Mitchell oljserved during the solidi- 

 fying of carbonic acid. This physisist informs us that when the acid 

 becomes liquid by pressure and esca})es from the vessel which contains 

 it, the solid which it forms receives positive and the receptacle nega- 

 tive electricity. [This article was written before the publication of the 

 researches of Faraday on the electricity of steam, which conclusively 

 prove that the excitement is due to the friction of the particles of water, 



'' Voyages dans les Alpes, touie II. sec. 807, page 228, et suiv. 

 f Annales de Chimie et de Physique, tome VIII, p. 161, 1818. 

 lAnnales de Chimie et de Physique, tome VIII, p. 161, 1818. 

 ^PhUos. Magaz., vol. XVU, page 374, 1840. 



