Prof. Forbes on the Pyro-electricity of Tourmaline. 133 



whole, than his theory of gaseous bodies and of vapours ; 

 which, had he done nothing else, would have placed him at 

 the head of modern physical inquirers in this, and in every 

 other country. I remain, Gentlemen, yours, &c. 



Sackville-Street, July 18, 1834. W. Prout. 



XXII. An Account of some Experiments on the Electricity of 

 Tourmaline, and other Minerals, when exposed to Heat. By 

 James D. Forbes, Esq., F.R.SS. L. 8? Ed., Professor of 

 Natural Philosophy in the University of Edinburgh* . 



\ LTHOUGH the phenomena of the pyro-electricity of 

 <*% minerals, as it has been termed, and those of the tourma- 

 line in particular, have, after a long period of neglect, been 

 recently studied by more than one philosopher of eminence, 

 there is a sufficient number of undetermined or debatable 

 points, even at the threshold of the inquiry, to yield facts of 

 novelty and interest to those who will take the trouble to look 

 for them. 



Having during the past summer been much engaged in 

 studying the relations of bodies to heat and electricity, I was 

 induced, by having in my possession a considerable number 

 of long tourmalines, to repeat and endeavour to verify some 

 recently published experiments with this mineral. These in- 

 quiries brought out several new facts; and, with the hope 

 of adding something to our knowledge in this curious field, 

 I have taken this opportunity of communicating to the Society 

 the results of some very recent experiments. 



My attention was principally directed to the verification 

 and extension of the views of M. Becquerel, whose ingenious 

 papers published in the Annates de Chimie for 1828, give us 

 almost the only information, with the exception of a short 

 paper by Dr. Brewster published in 1824, which we have 

 gained on this subject since the appearance of the works of 

 Haiiy. The undecided state in which several points of the 

 first importance were left by the philosophers of the last cen- 

 tury is not a little remarkable. In fact, the answer to the 



* From the Transactions of the Royal Society of Edinburgh, vol. xiii. 

 This paper was read before that Society on the 3rd of January 1832: the 

 author explains as follows the delay in its publication : 



U The publication of this paper was delayed partly under the idea of 

 prosecuting the experiments of which it contains an account j but the 

 author having engaged in some other researches, which appear to him of 

 more immediate importance, he merely prints this communication in its 

 original form. — April 1834." 



