[ 334 } 
their eledtrical inquiries with more certainty, fuc- 
cefs, and fatisfadlion. 
A profpedt of difcovering the caufe of the com- 
mon uncertainty in the adtion of eledtrical machines, 
induced me, fome months fince, to make fome 
obfervations on the appearances produced by a ma- 
chine in motion. Being well convinced, that the 
eledlric fire, which we receive from a machine, is 
derived from the cufhion, and from fuch parts as 
communicate with if, I firft attended to the eftedis 
which the glafs and rubber bad on each other. 
My inquiries, however, were not diredted to- 
wards an inveftigation of the caufe of that accu- 
mulation of eledlric matter, in confequence of the 
fridiion of the glafs on the rubber, as I looked on 
that circumfiance as a fecret in nature, no lefs 
penetrable than gravitation itfelf; but I endeavoured 
to find out the beft method of increafing the exci- 
tation of a glafs, -and of taking from it that fire for 
eledtrical purpofes which might be colledted on its. 
furface. 
It is evident, that the eledlric matter is excited 
in the inflant that the glafs pafies over the rubber,, 
and that it becomes fenlible to us by its adhering to 
the revolving furface of the glafs. It likewife ap- 
peared to me highly probable, that the quantity 
of fire, which we find on the glafs in motion, is 
not the whole of that which is excited by the paf- 
fage of the glafs on the rubber. The luminous ap- 
pearance in the angles between the glafs and rubber, 
and which is extremely diftindt in a dark room,, 
rendered it next to certain, that a part of the ex- 
cited eledlric fluid returns, immediately to the 
cufhion 
