26 Prof. Forzes’s Experiments on the Electricity of Tourmaline 
by Dr Brewsrer, published in 1824, which we have gained on 
this subject since the appearance of the works of Havy. |The 
undecided state in which several points of the first importance 
were left by the philosophers of the last century, is not a little 
remarkable. In fact, the answer to the fundamental question, of 
whether the tourmaline must be in the act of changing its tempe- 
rature, in order to the development of electricity, may be con- 
sidered to rest on the authority of Becqurret (who answered it 
in the affirmative), former authorities being divided upon it. 
Dr Tuomsoy, in his work on Heat and Electricity, published in 
1830, observes that “ when the tourmaline is once excited by 
heat, it retains its electricity for a long time, if care be taken to 
place it upon non-conductors. Aiprnvus found it electric after 
an interval of six hours*.’ He adds in a foot-note, “ These 
facts, as stated by Alpinus, if accurate, seem inconsistent with 
the statement of Canron and Brcqueret, that the electricity 
is only developed whilst the stone is changing its temperature.” 
A statement of Dr Brewsrer’s might also appear to support 
the views of Aipinus, and by opposing that of BecquERret, leave 
the question still undecided. He mentions J, that a slice of tour- 
maline cut transversely to the axis of the crystal, and placed 
on a plate of glass heated to 212°, adhered to it for six or eight 
hours, even when the glass was uppermost, the electricity of the 
tourmaline thus supporting its own weight. 
The experiment which I am about to describe, will I think 
set at rest the question, and is in fact capable of shewing within 
a few minutes, and ina very pleasing manner, the most essential 
facts of the relation of the electricity to temperature. M. Brc- 
auEREL found that when a crystal of tourmaline was heated to 
212°, its electricity was inappreciable so long as the temperature 
remained stationary ; but that when placed in a cooler medium, 
the intensity of the electricity was not, as might have been ex- 
* P. 478. + Edinburgh Journal of Science, i. 211. 
