of Electricili/ bij Pressure. 209 



the bodies, will be exactly that due to the remaining pressure. 

 Let us take, for instance, two insulated bodies, such as a disk 

 of cork and a crystal of sulphate of barytes, conveniently dis- 

 posed ; let us press them one against the other with the pressure 

 7>;let us diminish the pressure by the quantity jy'; the two bo- 

 dies will then be subject to the action of a pressure/? — p': let 

 us immediately withdraw the two bodies from the compression, 

 and we shall find upon each of them an excess of the contrary 

 electricity greater than that relative to the pressure j9 — p'. It 

 is evident that this plus value is solely attributable to the ces- 

 sation of the pressure, since the bodies have not ceased to be 

 in contact. 



The two fluids developed by pressure are pei'fectly in equi- 

 librium at the ."iurface of contact; for I have ascertained by 

 very accurate experiments, that neither of the two bodies, 

 during the continuance of the pressure, gives the least sign of 

 electricity. It may be generally asserted that the better con- 

 ductors bodies are, the greater ought to be the rapidity of their 

 separation, in order to prevent the two fluids from recombining: 

 it is probable that in the case of those bodies which are jierfect 

 conductors of electricity, the rapidity of separation ought to 

 be infinite. 



The following experiment gives an idea of the influence of 

 the rapidity of separation on the development of electricity. 

 Press an insulated disk of cork on an orange, and withdraw it 

 quickly ; it will retain a pretty considerable excess of viti'eous 

 electricity: but if instead of withdrawing the disk quickly, it 

 is done more or less slowl}-, it is regularly perceived that 

 the quantity of electricity developed by the same pressure, di- 

 minishes in proportion as the rapidity diminishes, till it be- 

 comes imperceptible when that is much abated. 'We shall 

 hereafter mention an apparatus, by the assistance of which 

 these experiments may be repeated with great accuracy. 

 We shall see that there exists for every substance and 

 for every pressure a degree of rapidity which gives a maximum 

 of electricity. 



From these considerations it may be afiirmed, that any two 

 bodies whatsoever, whether conductors or non-conductors of 

 electricity, being pressed one upon the other, always enter into 

 two different electric states; but these bodies, after their sepa- 

 ration, possess the quantity of electricity due to the pressure, 

 only in proj)ortion as the ra})idity of their separation is suitably 

 adapted, that is to say, is sulHcient to prevent the recombina- 

 tion of the two fluids. 



Caloric appears to have great influence in the phamomena 

 at present under our notice, since it modifies them in a very 



Vol. 62. No. 305. Sept. 1823. D d peculiar 



