208 M. Becquerel on the Development 



On the Causes -which modify the Development of Electricity by 

 Pressure. 



In the account I liave just given of the electrical phaeno- 

 mena produced by jiressure, I have only pointed out the 

 manner of repeating the experiments, without speaking of the 

 causes which might possibly modify the results : but as these 

 causes have more or less influence on the development of 

 electricity, and may even sometimes render it null, it is neces- 

 sary to examme them. 



The more or less perfect conducting power of the two 

 bodies subjected to pi-essure, has a singular influence on the 

 quantity of electricity produced. If, for instance, a disk of 

 elder-pith and one of metal are pressed together, neither of 

 tliem, when the pressure is withdi'awn, will be found to have 

 acquired any excess of electricity ; and this will be the case 

 whenever the substances pressed are conductors; each of these 

 substances will possess only the quantity of electricity due to 

 the contact. In general, it appears that the more perfectly 

 the two bodies possess the quality of conductors, the more 

 difficult it becomes to obtain electricity by pressure. 



We are ignorant of what passes during this action: never- 

 theless the electric phaenomena we have observed, permit us 

 to hazard some conjectures on this subject. It appears, that 

 at the moment of pressure there is produced a new state of 

 equilibrium between the two fluids which compose the natural 

 electric fluid ; the vitreous electricity takes possession of one 

 of the surfaces in contact, and the resinous electricity of the 

 other. As long as the pressure continues, tliese two fluids 

 are neutralized by each other, and they cannot escape from 

 the surface of contact. Thus, notwithstanding the reciprocal 

 attraction of their molecules, notwithstanding their greater or 

 less tendency to pass from one body to another, they find in 

 pressure, and in pressure alone, a power which neutralizes both 

 these actions. In fact, if the bodies be perfect conductors, as 

 soon as a diminution of pressure takes place, the two fluids in- 

 stantaneously combine, however great may be the rapidity of 

 the separation : if, on the contrary, one of the two bodies be an 

 imperfect conductor, a diminution of pressure is not immedi- 

 ately succeeded by the recomposition of the two fluids, the de- 

 vevelopment of which arose fi'om the cessation of the pressure. 

 This recomposit'on will occupy more or less time in the ratio 

 of the conducting power of the two bodies subjected to pressure; 

 so that, in the end, the quantity of electricity found in each of 



the 



