ATMOSPHERIC ELECTRICITY. 303 



tralized; it can only take place wlien tliey possess an excess of one or 

 the other electricity which is the same as that of the stratum where 

 they are found. If the particles possess a greater excess of this same 

 electricity they will act only in virtue of this excess upon each other 

 and upon all the molecules of the surrounding air; they must then 

 mutually repel each other. If, on the contrary, the excess of elec- 

 tricity v/hich they possess is less than that which they naturally re- 

 ceive in the position where they are placed, the mass of the medium 

 ■will act on each one of them by virtue of this diiference, and their 

 natural electricities will he decomposed as much as is necessary to 

 complete what is wanting to them of the electricity of the medium; by 

 virtue of this addition they repel the medium as much as the medium 

 repels them, and will therefore undergo no more action. But they act 

 on each other v/ith the excess v.^hich they have acquired from the 

 opposite electricity, and if the medium is an indefinite fluid composed 

 of particles susceptible of being electrified by contact, this excess will 

 by degrees be dissipated in space." 



Experiment does not sustain this mode of regarding the action of 

 the electrified air on the conducting bodies which are immersed in 

 it; for it would follow that an electrometer ought to present almost 

 always a negative divergence at the instant of its exposure to the air 

 under a serene sky, since its leaves would act on each other with the 

 excess of the electricity which they had acquired by the positive influ- 

 ence of the stratum of the surrounding air. It would likewise follow 

 that if, after having freed the instrument of its negative electricity, we 

 should lower it or raise it suddenly the leaves would exhibit a posi- 

 tive divergence in the former case and a new negative divergence in 

 the latter. Now, experiment shows that precisely the contrary takes 

 place. Other phenomena, of which we shall have occasion hereafter 

 to speak, are equally irreconcilable with tlie principle announced by 

 M. Biot. 



In his explanation of the formation of thunder clouds, M. Guy Lus- 

 sac* supposes that the electricity is diff'used in the atmosphere, and 

 that it exists in a free state, ready to be transferred and collected on 

 the conductors which are presented to it. On thi« supposition the 

 electrometer would always take a quantity of electricity corresponding 

 with that existing in the air into which it is immersed ; but this elec- 

 tricity cannot be the cause of the positive divergence which is observed, 

 since the surrounding air and consequently the armatures and the 

 gold leaves of the instrument being then in the same degree of elec- 

 trical tension, there is no reason why the last acted on by equal forces 

 should diverge from each other. This appears from the following experi- 

 ment, for which we are indebted to M. Peltier. f This scientist took 

 a glass globe covered with tin -foil, with the exception of two small 

 openings opposite each other so as to see what passed within. At 

 the centre of this globe he placed a small electroscope, the gold leaves 

 of which corresponded to the visual ray, crossing the tv>^o openings ; 

 he then charged the globe with a considerable quantity of electricity, 



« Ann. de Ch. ct de Phys., tome VIII, p. 163. 1818. 



■j-Obseiv. et Iiccherch. Exp^rim. , sur les Trombcs. introduction, p. 3. 



