316 ATMOSPHERIC ELECTRICITY. 



the sides of t"he vessel in which the evaporation takes place ; and that, in 

 all other circumstances, we do not observe a trace of electricity what- 

 ever may be the quantity of vapor produced. Thus, in evaporating in 

 a capsule of platina heated and connected with its electrometer a drop 

 of a solution of sea water partly saturated, M. Peltier found that there 

 is rarely a sign of electricity in the first experiment ; but, if we re- 

 commence without having cleansed the platina, the saline layer left by 

 the first drop being taken up by the second, and saturating it in a 

 higher degree, the latter becomes nearly opake when it is reduced to 

 a third of its volume. We then see a multitude of^ little bodies 

 swimming in it, and, soon after, we hear decrepitations attended with 

 saline projections which at the same instant produce in the electrome- 

 ter a negative deviation. If the platina is sufficiently cooled to admit 

 of being moistened, the decrepitation ceases, the drop extends and is 

 at once reduced to vapor. Now, M. Peltier observed that this sudden 

 eva^^oration, instead of increasing the electrical deviation, took away 

 a part or the whole of what had been produced during the decrepitation. 

 A third experiment produces a yet greater effect ; the decrepitation 

 is stronger and the needle forcibly deflected by the intensity of the 

 manifestation. 



It follows, therefore, that evaporation is only an adjunct in the elec- 

 trical excitement, and that the electricity is due to the chemical 

 decomposition of the hydrated molecules which adhere to the metal 

 possessing a high temperature. Thus M. Peltier obtained the same 

 result by substituting ibr salt water sea salt itself; this latter decrepi- 

 tating without any aqueous fusion, the water between the molecules 

 performing the part of the saturated solution, caused the needle of 

 the electrometer to move. If, on the contrary, we use a salt that is 

 unaffected by heat, and nearly insoluble, such as the carbonate of 

 barytes, there is no electricity produced, either with or without water. 

 Thus it appears that it is at the very moment of the separation of the 

 combined molecules of water that the electricity is produced, and not 

 during the evaporation of the superfluous water, as M. Pouillet believed. 

 When this separation takes place slowly, an electric neutralization 

 is produced before the molecules of vapor are sufficiently separated 

 from the liquid to retain the electricity which they had at the moment 

 of their formation ; while the sudden explosions produce the isolation 

 necessary to the preservation of the electricity developed. We know, 

 in fact, that when the two electric fluids are separated from each other 

 simply by chemical action, they always tend to unite again to form a 

 neutral state, through the conducting bodies which are present. 



The difference between the results^ to which M. Pouillet and M. Pel- 

 tier arrived may be exjdained, perhaps, by that of the instruments 

 which these two philosophers employed. The first used a condenser of 

 gold leaf; he observed no signs of electricity except at the instant of 

 the separation of the plates of the instrument ; and the electricity 

 which it then indicated was that which, being produced during the 

 decrepitation of the substances used, had remained disguised by the 

 opposite electricity of the upper plate. M. Peltier appears to have 

 made his experiments with his electrometer without a condenser. By 



