.[ 673 ] 
be at leafV as much. If not more, overcharged, when 
feparated, as if it is feparated all at once. 
In like manner, it fhould feem that the plate E/ 
will be confiderably undercharged, when feparated 
from the glafs, but not fo much fo as when in con- 
tact with it. 
Ftom the lame kind of reafoning I conclude, that 
if the repulfion is inverfely, as fome lower power of 
the diftance than the fquare, the plate will be 
confiderably undercharged, and E f confiderably over- - 
charged, when feparated from the glafs, but not in 
fo great a degree as when they are in contaa; with it. 
§ 7. There is an experiment of Mr. Wilke and 
^pinus, related by Dr. Prieftly, p. 258. called by 
them, eledlrifying a plate of air: it confided in placing 
two large boards of wood, covered with tin plates, 
parallel to each other, and at fome inches afunder. 
If a communication was made between one of thefe 
and the ground, and the other was pofitively elec- 
trified, the former was undercharged ; the boards 
ftrongly attraded each other j and, on making a 
communication between them, a Ihock. was felt like 
that of the Leyden vial. 
I am uncertain whether in this experiment the air . 
contained between the two boards is very much over- 
charged on one fide, and very much undercharged 
on the other, as is the cafe with the -plate of glafs » 
in the Leyden vial ; or whether the cafe is, that the '• 
redundant or deficient fluid is lodged only in the two . 
boards, and that the air between them ferves only' 
to prevent the eledricity from running from, one 
VoL. LXI. 4 R board 
