[ 446 ] 
the Tourmalin , never differed it to be in contact with 
any ( non elebtric ) body. 
Here, fay you, is a circumffancethat feems ofcon- 
iequence enough to caufe a fenfible difference; and then 
you appeal to the experiment which is to decide it: 
adding at the fame time, it is experiment that obliges 
and authorizes you to declare , that the rule advanced 
by you , is the only one that agrees therewith. Now 
your experiment tells us no more, than that you 
heated the Tourmalin in my manner, taking care 
(as you exprefs it) that it was in contadt with nothing. 
But notwithffanding this, that you have always found 
the event agreeable to your rule , and not one Jingle time 
to mine. 
From your defcription of this experiment, your 
exadt method of making it does not appear. I am 
inclined tobelieve fome material circumffance has been 
omitted in the method ; or thatour apparatus’s are effen- 
tially different; (though you feem to have had a regard 
to fome of the neceffary requifftes for making the 
experiment properly:) otherwife, I cannot appre- 
hend why you were not able to fucceed : becaufe 
the experiment always anfwers with me. Perhaps 
the difference in the fize of our Tourmalins may 
have contributed towards caufing the different effedts. 
The Tourmalins I employed in the experiments with 
the fame , are above Jive times larger than yours : and 
muff therefore require a longer time in heating. Now 
the degree of heat given to my large Tourmalins , 
was much below that of boiling water; and there- 
fore I fupedt, that the fmall Tourmalins , you em- 
ployed, were made hotter ; whereas they ought to 
have 
