404 Mr. Nicholson’s Defcription of 
-loaded within on one fide, that it ferves as a counterpoife to 
the revolving plate, and enables the axis to remain at reft in any 
pofition. The other parts may be diftinCtly feen in fig. 2. The 
fhaded parts reprefent metal and the white reprefent varnifhed 
glafs. ON is a brafs axis, palling through the piece M, which laft 
fuftains the plates A and C. At one extremity is the ball D 
already mentioned ; and the other is prolonged by the addition 
of a glafs flick, which fuftains the handle L, and the piece 
GH feparately infulated. E, F, are pins rifing out of the fixed 
plates A and C, at unequal diftances from the axis. The crofs- 
piece GH, and the piece K, lie in one plane, and have their 
ends armed with fmall pieces of harpfichord-wire, that they 
may perfectly touch the pins EF in certain points of the revo- 
lution. There is likewife a pin I, in the piece M, which 
intercept a fmall wire proceeding trom the revolving plate B. 
The touching wires are fo adjufted, hy bending, that when 
the revolving plate B is immediately oppofite the fixed plate A, 
the crofs-piece GH connects the two fixed plates, at the fame time 
that the wire and pin at I form a communication between the 
revolving plate and the ball. On the other hand, when the 
revolving plate is immediately oppofite the fixed plate C, the 
ball becomes connected with this laft plate, by the touching of 
the piece K againft F ; the two plates, A and B, having then 
no connection with any part of the apparatus. In every other 
pofition the three plates and the ball will be perfectly uncon- 
nected with each other. 
Mr. Cavallo’s difcovery, fo well explained in the laft 
Bake rian LeCture, that the minute differences of electriza- 
tion in bodies, whether occafioned by art or nature, cannot be 
completely deftroyed in any definite time, may be applied to 
explain 
