38 Prof. Forbes's Experiments on Tourmaline^ fyc. 



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 obtained 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. 



GliEKNHILL, 



M January 1832. 



