Chemical Theory of Electricity and Magnetism. 57 



this account they may more forcibly attract the opposite one from the 

 air in their vicinity. 



It has long been known, that a siliceous stone called the tour- 

 malin, when its surfaces are polished, if it be laid down before the fire, 

 will become electrified with vitreous, or what is called positive electri- 

 city on its upper surface; and resinous, or what is called negative 

 electricity on its under surface; which I suppose lay in contact with 

 somewhat which supported it near the fire. 



In this experiment I suppose the tourmalin to be naturally com- 

 bined with resinous electric ether like glass; which on one side next 

 towards the fire by the increase of its attractive power, owing to the 

 heat having loosened its combination with the earth of the stone, 

 more strongly attracts vitreous electric ether from the atmosphere ; 

 which now stands on its surface : and then as the lower surface of the 

 stone lies in contact with the hearth, the less quantity of vitreous ether 

 is there repelled by the greater quantity of it on the upper surface; 

 while the resinous ether is attracted by it: and the stone is thus 

 charged like a coated jar with vitreous electric ether condensed on one 

 side of it, and resinous on the other. 



So cats, as they lie by the fire in a frosty day, become so electric 

 as frequently to give a perceptible spark to one's finger from their ears 

 without friction. 



A fourth method of separating the two ethers would seem to be by 

 the decomposition of metallic bodies, as in the experiment with Volta's 

 Galvanic pile ; which is said by Mr. Davy to act so much more power- 

 fully, when an acid is added to the water used in the experiment; as 

 will be spoken of below. 



From experiments made by M. Saussure on the electricity of evapo- 

 rated Avater from hot metallic vessels, and from those of china and 

 glass, he found when the Vessel was calcined or made rusty by the 

 evaporating water, that the electricity of it was positive (or vitreous), 

 and that from china or glass was negative (or resinous), Encyclop. 

 Britan. Art. Elect. No. 206, which seems also to show, that vitreous 

 electric ether was given out or pi'oduced by the corrosion of metals, 

 and resinous ether from the evaporation of water. 



