C 452 ] 
removing the 'Tourmalin into another room, to repeat 
the experiments we have here been treating of, I 
obferved it was electrified, j though no caufe for its 
being fo then appeared : the friction arifing from the 
air, in fuch circumftances, being not fufficient to pro- 
duce that effedt. And I muff here take notice, that 
many months before this fadt was afcertained, I fre- 
quently fufpedted the like appearance : but it happened 
at thole times that the effedts were fo uncertain, and 
appeared fo accidental, that I did not think they de- 
lerved attention -j-. 
In tracing out the caufe of this appearance, it feem- 
ed molt necelfary to obferve the changes in the air 
with refpedt to warmth : for, it is well known, thofe 
changes caufe manifeft alterations in the expanfion and 
contraction of bodies. 
EXPERIMENT I. 
In a room with a fouth afpedt, and where no fire 
had been for fometime, Farh. Therm, flood at 42. 
The Tourmalin was in the fame room, and had con- 
tinued there fome hours, undiflurbed, without fhew- 
ing any figns of eledlricity. On removing the Tour- 
malin into a warm room carefully, and the Therm. 
along with it, in lefs than 3 minutes (the Therm. 
having rifen to 47) the convex fide of the (lone fhewed 
f N. B. The experiments upon the Tourmalin , by Mr. Epi- 
nus, which refpedt the heating and cooling of its Tides equally , 
when occafioned by violent and artificial means , are, it is apprehend- 
ed, very different from the ten following experiments ; tho’ they 
alfo refpedt an equal heating and cooling of the {tone ; becaufe 
the degree of heat employed, is not only cxtreamly different, but 
the means of obtaining it, is fo likewife. The one being natural 
and the other artificial 
a minus 
