of Electricity by Pressure. 207 



cess of vitreous electricity. Even fruits, as, for instance, the 

 orange, being slightly compressed by the disk of insulated 

 cork, communicate to it an excess of vitreous electricity. In 

 proportion as the fruit dries, its power of electrifying the cork 

 diminishes. When ripeness has given it all the elasticity of 

 which it is susceptible, and before its surface is moistened by 

 decomposition, this power appears to be at its height. 



The insulated cork, applied with pressure upon all parts of 

 animals, provided they are not moist, receives an excess of 

 resinous electricity. The hair and fur of animals communi- 

 cate to it nearly as much as Iceland spar would do, but it is 

 of a contrary nature. 



Imperfect liquids, when sensibly compressible, give analo- 

 gous results. Cork, slightly pressed upon oil of turpentine 

 thickened by fire, exhibits, after the pressure, an excess of 

 resinous electricity. 



I have hitherto only considered the pressure of a disk of 

 cork upon different substances ; but similar results would be 

 obtained by the pressure of disks of leather, of amadou, or of 

 elder-pith, upon the same substances. 



Bodies which have acquired electricity by pressure, pre- 

 serve it for a longer or shorter time according to the degree 

 of their conducting power. M. Haliy found that Iceland 

 spar gave some signs of electricity, even at the end of eleven 

 days. There are other bodies, which are such good conductors, 

 that, when not insulated, they part with the excess of elec- 

 tricity they have acquired, to the substances with which they 

 are in contact. The sulphate of barytes of Royat is of this 

 number : it is necessary to insulate it perfectly, in order to 

 preserve its electricity. A crystal, which had been subjected 

 to the experiment, possessed the electric faculty at the end of 

 half an hour. It is very probable that the continuance of 

 electricity in bodies is in proportion to their conducting power. 

 This preservation of electricity in certain bodies, notwith- 

 standing the absorbing action of the air, and even notwith- 

 standing the contact of the moist substances by which they 

 are surrounded, has been satisfactorily proved by M. Haiiy. 

 May it not be accounted for by supposing that the electricity 

 developed by pressure at the surface of these bodies acts on 

 the natural electricity of their masses, decomposes it, attracts 

 that of a contrary denomination, and drives the other into 

 the centre of the mass, in such a manner as to transfoi'm these 

 bodies into actual condensers, precisely as when an electrified 

 plate is placed on the marble plate of Volta's condenser ? 



On 



