264- M. Becquerel 07i the Development 



different electrical states ; but this property lasts for a few mo- 

 ments only after exfoliation. If we wish to restoi-e it to them, 

 it is necessary to raise the temperature of one of the lamime. 

 From this it appears, that when two thin laminae of mica are 

 abrujitly separated, they are not both at the same temperature ; 

 since after some instants, that is to say, when an equilibrium 

 of temperature has established itself between the two laminae, 

 it is necessary slightly to heat the one in order that the pres- 

 sure may develop electricity. This agrees with our remarks 

 upon what takes place when two bodies identical in all re- 

 spects are pressed upon each other. It is much to be desired 

 that it could be immediately ascertained by experiment, whether 

 the temperature of each lamina is really the same immediately 

 after their separation. 



Sulphate of lime requii-es certain precautions before it can 

 be rendered electric by exfoliation ; it is first necessary to de- 

 prive it of its hygrometric water, and allerwards to raise its 

 temperature, in order to make the pha?nomena apparent. 

 The mode of development of electricity by exfoliation, appears, 

 with very few exceptions, to be adapted only to regularly 

 cr^'stallized substances: it is not the effect of mere rending; 

 for when a tube of glass, or a strip of lac, is broken, each part 

 is totally devoid of electricity. 



La'ws of the Dcvelopvicnt of Electricity by Pressure. 



We are ignorant, as yet, whether the cause of electric phaeno- 

 rtlena is a s})ecies of matter emitted, or whether it is merely the 

 result of a vibratory movement impressed on the molecules 

 of bodies: the uncertainty which prevails on this subject proves 

 that the phacnomena relative to the development of electricity 

 are still covered by a thick veil. Many important physical 

 properties of electricity are already known ; among others its 

 attractions and re]iulsions, and the laws according to which 

 they take place; its distribution over conducting bodies, 

 whether insulated, or subject to the influence of other electri- 

 fied bodies : but no investigation has yet been made into tiie 

 laws of the development of the electric principle; an inquiry 

 of that nature demands a mode of electrifying at once simple 

 and easily measurable ; such a means is Ibund in jiressure. 



We have shown, by a great number of expeiiments, that 

 two bodies conveniently disposed, and pressed against each 

 otlier, were found, when withdrawn from compression, to be 

 in different electric states ; that if exceptions to this rule 

 were found to exist, they proceeded merely from the want of 

 that degree of velocity in separating the bodies, which is ne- 

 cessary to prevent the two fluids from recombining ; and that 



in 



