[mall Quantities of ILleBr icily. 2 r 
If it be afked, what power communicates the electricity, or 
originally difturbs the equilibrium of the natural quantity of 
eleCtric fluid in the various bodies of the univerfe ; we may 
anfwer, that the fluctuating eleCtric date of the air, the paflage 
of eleCtrifled clouds, the evaporation and co;idenfation of fluids, 
and the friction arifing from divers caufes, are perpetually a Cl- 
ing upon the eleCtric fluid of all bodies, l'o as either to increafe 
or diminifh it, and that to a more confiderable decree than is 
generally imagined. 
I lhall laftly conclude, with briefly propofing an explanation 
of the production of eleClricity by friction, which is depen- 
dent upon tiie above dated proportion, viz. that bodies are 
always eleCtrifled in fome degree ; and likewife upon the well 
known principle of the capacity of bodies for holding eleCtric 
fluid being increafed by the proximity of other bodies in certain 
c ire um fiances. 
It feems to me, that the cylinder of an eleCtrical machine, 
like ABC in fig. 4. mud always retain fome electricity of the 
pofltive kind, though not equally denfe in every part of its 
furface ; therefore, when the part of it A is fet contiguous to 
the rubber fg, it muft induce a negative eleClricity in the 
rubber. Now, when by turning the cylinder, another part 
of it B (which fuppofe to have a lefs quantity of pofltive 
eleClricity than the preceding part A) comes quickly againft 
the rubber ; the rubber being already negative, and not being 
capable of lofing that eleClricity very quickly, muff induce a 
ftronger pofltive eleClricity in the part B, which is now oppo- 
fite to it ; but this part B cannot become more pofltively elec- 
trified, unlefs it receives the eleCtric fluid from fome other 
body, and therefore fome quantity of eleCtric fluid pafles from 
the lowed part of the rubber to the part B of the glafs, which 
additional quantity of eleCtric fluid is retained by the part B 
only 
