[ 33 r ] 
Tides of the ftone, and a minus one in the amber. 
Afterwards I electrified the amber, and held it near 
the Tourmalin ; ftill both fides were plus : and if I 
rubbed the Tourmalin whilft the amber was electri- 
fied, it continued plus . Then I rubbed the Jlone with 
glafs ; notwithftanding which, both fides of the T our - 
malm were plus , and the glafs minus . 
Exp. 31. But when the glafs was electrified plus, 
and held near the Tourmalin , as I had done before 
with the amber, in this cafe, both fides were electri- 
fied minus . 
Thefe experiments feem to fhew, that where elec- 
tric appearances are produced, by the rubbing of any two 
polijhed bodies together , that body, whofe fubftance 
is bar deft, and eledlric power JlrongeJl , will be always 
plus, and the j oft eft and weakeft , always minus . It was 
from this theory, with which I had the pleafure to 
acquaint you, that I was defirous of trying to elec- 
trify the Tourmalin minus by rubbing , not having at 
that time been able to do it. I fixed upon a brilliant 
diamond for this purpofe, as being the hardejl body, 
and JlrongeJl eletlric, that I was acquainted with ; 
and, upon rubbing the Tourmalin with it, my expec- 
tations were anfwered ; for both fides of the Tourma- 
lin were electrified minus , and the diamond plus, 
Exp. 32. Thefe experiments fucceeding, I rubbed 
glafs againft glafs, and found, that they elettrified 
each other ; but one of them was plus , and the other 
minus. 
Exp. 33. Two pieces of amber, treated in the fame 
manner, were alfo electrified plus and minus. 
Exp. 34. When I rubbed glafs againft amber, the 
former was plus , and the latter minus. 
~ U u 2 Exp. 
