404 PHILOSOPHICAL TRANSACTIONS. [aNNO 1759- 



with a small flat border round it. It was square, but one of the corners had 

 been broken off. When he examined it, the broken part was plus, and the 

 corner opposite to the broken part minus : so that here also the electric current 

 ran through the stone in a diagonal line. 



Exper. 5 1 . Every one of these tourmalins, except that in the British Mu- 

 seum, he greased all over, and, while they were warm enough to preserve the 

 grease liquid, he tried each tourmalin separately, but found no alteration in the 

 virtue of the stone, except weakening it a little; though it is well known, that 

 moisture of any sort readily conducts the electric fluid ; and therefore, if the 

 tourmalin had not a fixed kind of electricity, the plus and minus observable on 

 the two sides of the stone, must, by this treatment, have united and destroyed 

 each other : the plus side parting with as much of the fluid as the minus, on 

 the other side wanted to restore the equilibrium. 



Upon the whole, all these experiments do most clearly prove, that the tour- 

 malin suffers the electrical fluid to pass through it only in one direction, and so 

 far it bears some analogy to the loadstone. And as the loadstone loses its virtue 

 by being made red hot, he was desirous to see what would be the event in the 

 tourmalin under the same treatment. 



Exper. 52. He therefore put one of the flat tourmalins into a strong fire, 

 for half an hour : but could not afterwards perceive the least alteration. He 

 made the same experiment on another tourmalin, with the same success. 



Exper. 53. Lastly, he heated the stone again, and, while it was red hot, 

 he threw it into water ; by which treatment the virtue of the tourmalin was en- 

 tirely destroyed, and it had the appearance of being shivered in many parts, 

 without breaking. 



In regard to the internal frame of the tourmalin, we can say nothing ; yet so 

 much we have learned, by these experiments, that there are 3 different methods 

 of heating the tourmalin, which produce different electric appearances; that 

 different degrees of heat afford different appearances ; that friction has the 

 same effect on it, as on glass ; and that the tourmalin, when it is heated pro- 

 perly, suffers a current of the electric fluid to pass through it in one direction 

 only : so that the tourmalin hath, as it were, 2 electrical poles, which are not 

 easy to be destroyed or altered ; and further, that there is not any substance in 

 nature, which we are acquainted with, that the electric fluid does not readily 

 pass through ; that there seems to be a constant flux and reflux of it in all 

 bodies, as well in the air as in vacuo, occasioned by the alternate changes of 

 heat and cold in every part of this globe. 



