38 Prof. Forses’s Experiments on Tourmaline, &c. 
it required some attention to discover that the maximum inten- 
sity was not immediately gained. It lasted a short time, and, as 
in the case of slender tourmalines, the needle rapidly receded, 
and in a short time returned to zero. 
The very satisfactory results which I have obtamed from all 
these minerals, give me great confidence in the aptitude and ac- 
curacy of my simple apparatus ; and, from the very considerable 
intensity which I find them all to possess, I expect to be able to 
estimate much smaller degrees of pyro-electricity in other mine- 
rals, and in artificial crystals, than has yet been attempted. 
Should my first results have appeared interesting to the So- 
ciety, I may perhaps at no distant time have the honour of com- 
municating my farther progress in the inquiry. 
GREENHILL, 
2d January 1832. 
