194 APPENDIX TO MEMOIR OF PELTIER. 



doctrines. Now, the most important part of physics for meteorology, electricity, 

 dates back scarcely a contiuy. The discovery of the Leydcn jar by Miisschen- 

 broeck and Cmieus dates from 174G, the experiments of Dalibard and of Frank- 

 lin from 1752; what could meteorology be before that epoch? Evidently it 

 could consist only of theories, of suppositions more or less vague and unmeaning; 

 in fact, before that epoch, but little consideration was applied to it. It was 

 quite otherwise after the period in questi(m ; the discovery of Musschenbroeck 

 had aroused all thinking minds ; the analogy between the ek'ctric spark and 

 the thunderbolt appeared evident ; all the world threw itself with ardor into 

 the study of electrical phenomena on the one hand, and of meteorological phe- 

 nomena on the other ; a great number of savants devoted themselves to the 

 study of atmosidieric electricity, and if the results at which they arrived had 

 not at first all tlie precision that might be desired, they always maintained an 

 interest which fostered and kept alive the general attention. 



The number of savants who occupied themselves with experiments on atmo- 

 spheric electricity in the second half of the eighteenth century was very con- 

 siderable. Some of these, like Lemonnier, Ronayne, Read, Schiibler, made 

 use, by preference, of fixed apparatus, while others, like Romas, the prince 

 Galitzin, Musschenbroeck, Van Swinden, the duke de Chaulnes, Bcrtholon, 

 Franklin, Cavallo, joined thereto the use of the electrical kite. Beccaria, who 

 had at first experimented onl^' with fixed apparatus, employed also the electrical 

 kite at a later date. 



The results at which these savants arrived were most contradictory. Romas, 

 Galitzin, Musschenbroeck remarked from the beginning that the electric signs 

 varied with the course of the kite ; on the other hand, Beccaria, Read, Schiib- 

 ler, complained of the little accordance of the fixed appar.atus ; hence it was 

 impossible to reach a conclusion even approaching certainty. Yet, as doubt is 

 always painful to the human mind, it came to be admitted generally, on the one 

 part, that the air Avas electrical ; on the other, that the electricity of the air 

 proceeded from the evaporation which takes place at the surface of the soil. 

 For the substantiation of this opinion, reliance was placed on the old experi- 

 ments of Volta, Lavoisier, and Laplace, and on the more recent ones of M. 

 Pouillet. These experiments consisted in projecting water on a body raised to 

 a high temperature ; but it was M. Pouillet alone who had employed a crucible 

 of platina in place of an oxidizable metal as the other physicists had done. In 

 these experiments the vapor formed, almost always yields electricity, and when 

 it does so it is always vitreous electricity. 



The first thing which Peltier did was to repeat, while he also simplified, the 

 experiment of Pouillet, and he showed that the formation of vapors only gives 

 an appreciable electricity when the vase has a temperature of at least 110 

 degrees ; that below that temperature the instruments can no h)nger collect any, 

 and that, in fine, even at that temperature they can only collect it when there 

 has been calefaction and then decrepitation of the drop of water projected.* 

 The high temperature and the assemblage of phenomena necessary to maintain 

 separate the electricities produced, never meet together in our ambient medium ; 

 never does the vapor, when it rises on the surface of the soil, possess any con- 

 siderable tension ; hence spontaneous evaporation gives no electrical signs, 

 unless under circumstances wholly peculiar. 



Spontaneous evaporation being incapable of communicating electricity to 

 vapors, and those of the atmosphere containing considerable quantities of it, 

 Peltier felt engaged to seek the true origin of that electricity. He recuiTed, 

 therel'ore, to an old experiment of Saussure and Ermann, which in their hands 

 had been barren of results ; and as this experiment may be considered as the 



* See the note of Peltier contained in rinslitut, vol. ix, p. 31 ; and his memoir on atmo- 

 spheric electricity, Ann. de Chim. et de phys., 3 series iv, p. 383. 



