84 On the Electricity of Minerals. 



tion. If it repels the pole of the tmirnnaline to which we 

 first present it, this onlv imlicates that the body is itself in 

 the electric state, and a!?o that its electricity is contrary to 

 that of ihe pole in question. But if the tourmaline was 

 attracted, we could conclude nothing from it, because a 

 body which is even in the natural state, acts always by at- 

 traction on an electrized body, whatever be the kind of 

 electricity which this last requires. In this case, therefore, 

 we must afterwards present the body to the other pole of 

 the tourmaline ; and if the repulsion succeeds the attraction, 

 we shall have a proof that this body is in a state opposite 

 to that of the pole which has been repelled. 



When we employ the electricity acquired by heat, solely 

 as a mineralogical character, the small metallic needle re- 

 presented (fig. 1.) is sufficient for the experiments relative 

 to this character, without its being even necessary to isolaie 

 this needle. We judge that a mineral is endov\ed with the 

 property in question, according as it attracts the needle to 

 it, or leaves it fixed when placed at a small distance from it. 



I recently made use of this method for comparing various 

 minerals, relative to the faculty which tbev have O'f pre- 

 serving for a longer or shorter time the electricity acquired. 

 by friction. After having put them in the electrical state, 

 I placed- them on any stone, (marble for instance,) so as 

 to make the surface which had been rubbed, opposite to 

 that which lay upon the stone, and I'rom time to time I 

 took them with my fingers or with pincers, by a corner 

 which was far from the electrized part, in order to present 

 them to the small needle. The topaz, of all the minerals 

 which I tried, seeiried to preserve electrrcity longest. A cut 

 piece of the limpid Brazil kind acted upon the needle at 

 the end of 32 hours. In the hyaline corindon, called 

 oriental sapplme, the emerald, the spinel, and other stones 

 which are made into trinkets, the duration of the electrical 

 virtue generally exceeded five or six hours: it exceeded 24 

 hours in an emerald from Peru. But I met with two mi- 

 nerals which difier from the above in a striking manner bv 

 a less coercive force with respect to the electrical fluid, — the 

 one is the diamond and the other rock crystal, — and I re- 

 marked that their e-lectrical virtue was extinct in 15 or £0 

 minutes. Some crystals of quartz, however, preserved it 

 for about 40 minutes. 



The limpid Brazil topaz, already mentioned, seems to re- 

 semble the diamond in the liveliness of its lustre, where it 

 has been cut. It is the same with the hyaline corindon 

 caWQ&white sapphire. . The foregoing results might be em- 

 ployed 



