of Electricity by Pressure. 



271 



We see then that for the pressures 



1 



2 

 3-4 



3 

 4-6 



4, 

 6. 



the electric intensities are x 



The electric intensities are then sensibly proportional to the 

 pressures; for if we suppose ^'=1-5, we shall have results 

 which would differ very little from those given by experiment. 



Pressures 12 3 4, 



Calculated elect, int. 1-5 3-0 4-5 6. 



Polished Iceland spar, subjected to the same experiments as 

 cleaved Iceland spar, has constantly given, for the same pres- 

 sure, a quantity of electricity weaker than the latter, in the re- 

 lation of two to six ; that is to say, that in polished Iceland spar 

 the electric faculty, by pressure, is about one third of what it 

 is in the same substance in its natural state. This difference 

 is remarkable, for the polish of mineral substances usually in- 

 creases the electric faculty; while in Iceland spar it dirni- 

 nishes it. The hygrometric state had no influence in this dif- 

 ference, since the crystal was deprived of water before the ex- 

 periment. 



Let us submit other substances to pressure : 



Substances 



