APPENDIX TO MEMOIR OF PELTIER. 179 



After having sufficiently verified tins fact, Peltier sought to find whether it was 

 the consequence of a special force or the result of a permanent electric state, 

 and he ascertained that in their natural state, or that of equilibrium, bodies pos- 

 sess different quantities of static electricity, and that consequently the proximity 

 of a metal which, like platina for instance, is negative in its natural state of 

 equilibrium, influences the neighboring bodies, rendering them more positive, 

 and, in consequence, more apt to receive and retain positive electricity. From 

 this it results that two condensing plates, the one of gold, the other of platina, 

 influence one another ; the platina renders the gold more apt to receive and 

 retain positive electricity, and the gold renders the platina more apt to receive 

 from it negative electricity. If these two plates be placed in contact they take 

 reciprocally that electricity for which they have most aptitude. 



We must not confound this peculiar property of the metals with the electro- 

 motive force of Volta. Contact is here of no account, for the same results are 

 obtained without contact, only in this case the results are somewhat lessened by 

 the distance. 



After having verified these facts, Peltier expressed them in the most general 

 manner, by saying that the metals have diflEerent capacities for collecting the 

 same static electricity from a constant source. But it was impossible for him to 

 arrive at the cause of this difference. Since that time, the researches of M. de 

 la Rive, and especially those of M. Edmond Becquerel, would seem to have suf- 

 ficiently elucidated the proldem. These two savants have demonstrated in effect 

 that the metals least liable to be tarnished are yet, in reality, oxidized in the 

 open air; but very slowly and very slightly, which had theretofore prevented 

 the physicists from perceiving it. The quantity of platina oxidized is unques- 

 tionably very minute, but the experinients of Faraday, of Peltier, and of Bec- 

 querel have proved that it needs but the oxidation of an almost imperceptible 

 quantity of metal to produce considerable quantities of static electricity; if, 

 therefore, platina is always naturally negative in relation to gold, it is because 

 it oxidizes to a greater degree ; if it is also negative in relation to zinc, this is 

 referable to the fact that tlie zinc employed is always covered with a coat of 

 oxide which preserves the metal from all ulterior alteration. 



Modifications in the torsion balance. — For a long time there was nothing avail- 

 able for the purpose of indicating the tension of static electricity, except the 

 gold-leaf electrometer and the torsion balance. The fornrer instrument possesses 

 great sensibility, but unfortunately does not afford a measure ; the latter, on the 

 contrary, gives"^ exact measures, but has not the sensibility requisite for delicate 

 experiments ; it has besides some serious defects. Peltier adapted to the torsion 

 balance modifications which eliminated these defects, and designed, besides, an 

 electrometer which unites the precision and measurement of the torsion balance 

 with the sensibility of the best gold-leaf electroscopes. We shall speak in suc- 

 cession of the torsion balance, as modified by Peltier, and of his electrometer. 



The torsion balance, as it was employed by Coulomb, had the inconvenience 

 of not maintaining in electric equilibrium the two balls between which the elec- 

 tricity under experiment is distributed. When one of the two loses more than 

 the other, whether by reason of its own asperities or that of the neighboring 

 bodies, the humidity of the air and the imperfect insulation of the supports 

 which is the consequence thereof, or through whatsoever other accidental cause, 

 there results an inequality of action, of which the resultant is no longer the 

 expression of the repulsive quantities alone; for as soon as the inequality of 

 charge supervenes, the action becomes complicated from the repulsion of the 

 similar electricities, and from the attraction produced by the excess of one of 

 the balls over the contrary electricity of the other ball, which the former devel- 

 opes by influence. 



With a view to avoid these causes of eiTor, Coulomb took infinite precautions 



