M. Becquerel on the electrical properties of Tourmaline. 51 



were the subjects of very long discussions. It was thus that 

 ^pinus asserted, that if, one side was heated more than the 

 other, they each acquired an electricity opposite to that which 

 was natural to them ; while Wilson maintained, that, when the 

 sides of the tourmaline were heated unequally, that side which 

 had the highest temperature took the electricity which was pro- 

 per to it, and transmitted it to the other side. A contradiction 

 so palpable must result from a difference in the manner of 

 making the experiments. They attempted to remove it by 

 making new experiments, but not succeeding, they each thought 

 they were in fhe right, and employed themselves no longer on 

 the question, which since then has ceased to attract the atten- 

 tion of natural philosophers. 



At that period tourmalines, which were only procured in 

 India, were rare in Europe ; and hence the same stone passed 

 in succession through the hands of Canton, ^pinus, and Priest- 

 ley, in order to study its properties. At present they are very 

 common, since the discovery of a stratum in Spain which con- 

 tained a great quantity of them. Canton, in a paper read to 

 the Royal Society of London in December 1759, asserted, to 

 use his own expression, that the tourmaline neither emits nor 

 absorbs the electrical fluid but by the increase or diminution 

 of the heat. This fact, which should have fixed the attention 

 of philosophers, has been entirely forgotten. 



The same philosopher has added another important fact to 

 the theory of the tourmaline, by showing, that, if a crystal is 

 broken at the moment when it is electrical, each piece possesses 

 equally two poles, in such a way that the two separate parts 

 are in two different electrical states. He has also discovered 

 that the topaz of the Brazils, and many other crystallized 

 mineral substances, possess electrical properties analogous to 

 those of the tourmaline. In the treatises on natural philosophy 

 there is very little said about the tourmaline. Even M. Haiiy, 

 who attaches great importance to the physical characters of 

 mineral substances, on account of the application which he made 

 of it to mineralogy, his favourite science, has given but an 

 incomplete theory of the tourmaline. He has, however, discover- 

 ed one important fact, that the crystals which derogate from 



