[ 3M- 3 
in the year 1 7^6, the former of whom it is well 
known Could never come into it*. And I am ftill the 
lefs inclined to alter my opinion of this matter, from 
an acquaintance with the properties of the Tourma- 
lin , which I think has furnifhed me with fufficient 
grounds for advancing that Dr. Franklin is miftaken. 
I have wondered that JEpinus did not take notice of 
fome of the experiments which eledtrify glafs either 
plus or minus , becaufe the Tourmalin affordeth lead- 
ing experiments towards it ; and can afcribe it to no 
other caufe than a favourable opinion he was willing 
to entertain of Dr. Franklin's hypothecs. 
To prove that glafs is permeable by eledtricity, I 
took a very large pane thereof (I chofe it large, that no 
objection might be made to the experiment) and then 
warmed it a little, fo that it was free from moifture. 
After that, I held it upright by one edge, whilft the 
oppofite edge refted upon wax, and rubbed the mid- 
dle part of the furface with my finger. After this, I 
found that both fides were eledtrified plus. . Upon 
repeating the experiment many times, with different 
glafs and different degrees of rubbing, ftill both fides 
were in every experiment eledtrified plus . Now they 
could not both be eledtrified plus by this treatment, 
unlefs fome part of the fluid had really paffed through 
the glafs j becaufe the virtue could not get round to 
the other fide over fo great a furface: befides, the ex- 
tremities of the glafs were not eledtrified at all. As 
to eledtrifying glafs minus, I find it may be done 
three different ways. But thefe and other experi- 
ments relating to the permeability of glafs, I fhall 
* Vid. Icttres fur l’e&ricite par M. l’Abbe Nollet, lett. iv. 
forbear 
