of Electricity by Pressure. 265 



in the case of two perfect conductors, the velocity of separa- 

 tion ought to be infinite. 



The development of electricity by pressure is modified, as 

 we have seen, by the nature of the bodies ; by the state of 

 their surfaces ; by their hygrometrical condition, the degree of 

 the pressure, the velocity of the separation, and the tempera- 

 ture. It is necessary then to study the influence of each of 

 these causes, in this development, if we desii-e to discover the 

 electric phaenomena which relate to them. 



The researches concerning the development of electricity 

 have hitherto been confined to the discovery of the means of 

 setting in motion the electric principle, and the inquiry into the 

 circumstances under which this phasnomenon was modified; 

 but it has never been attempted to measure its effects when 

 one of the influential causes varied. It is certainly something 

 to discover a phaenomenon ; but the question is only half re- 

 solved, if the law according to which it operates is not also 

 discovered; this law comprehends in its extent all the par- 

 ticular cases, which then become immediate consequences 

 of it. 



We know, for instance, that friction, heat, evaporation, &c. 

 are so many agencies by which electricity is disengaged ; but 

 what is the intensity of this disengagement when the fi'iction 

 is more or less rapid, when the temperature is more or less 

 elevated? Of this we are still in ignorance. Friction, which is 

 a compound phaenomenon, is less adapted to inquiries of this 

 nature than pressure, which is a more simple mode of action. 

 We can, in fact, increase or diminish its intensity by a de- 

 terminate value ; and on comparing the quantities of electri- 

 city which result from it, we must deduct from them the re- 

 lation between the pressures and the corresponding electric 

 intensities. This relation constitutes one of the laws of the 

 development of electricity by pressure. I shall take occasion to 

 observe, in the sequel, that pressure being one of the elements 

 of friction, it is natural to examine, in the first place, the na- 

 ture of its action upon the phaenomena, in order to be after- 

 wards qualified to draw some inferences concerning the de- 

 velopment of electricity by friction. 



Description of the Apparatus for measuring the electric Effects 

 produced by Pressure. 

 Inquiries like that in which we are engaged, require an ap- 



{)aratus by means of which the causes which influence the deve- 

 opment of electricity may be varied, and their effects measured, 

 at pleasure : for the present, however, we shall attend to the 

 variation of one only of the influential causes, and shall sup- 

 Vol. 62. No. 306. Oct. 1823. L 1 pose 



