Quadrant-Electrometer. 299 
&c., are not in accord within the limits of errors of observa- 
tion, using these equations of capacity; but they are in better 
adC 
TRC i have 
no explanation of this to offer; but in what follows it is 
assumed that the equations expressing the facts are 
AC 
?=p(A—B), where P= EGP ] 
Q= guA—gqueB—gquD + bye, 
Qo= — GA + J22B—924D — Bud, 
Qu=— quA—quB+ quD. | 
We are now in a position to determine the various coeffi- 
cients of capacity : in doing so it is necessary to distinguish 
the values of g;; and g. when the posts by which contact 
with the quadrants is made are down and in contact with the 
quadrants, and when they are raised up out of contact ; the 
former are denoted by q4,+4 and qo.+<a, the latter by g,, and 
22, the capacity of the binding-posts being a. As a convenient 
temporary unit of capacity the value of Gu’, when the jar has 
the standard charge, istaken. The first set of experiments 
was to determine the deflections caused by known potentials 
with varied charge ofjar, one or other of the quadrants being 
insulated. Three potentials of the jar were used—that of the 
standard indicated by the idiostatic gauge and two lower. The 
values of are denoted by wz, M2, Hy. It was found by con- 
necting the two quadrants to standard cells that 
Pay iy 2 O00 > O'o800 
accord if, in lieu of the term «9C, we write 
and hence 
Bp2=1, Bu2=0°648, Bu? =0°342. 
Suppose quadrant A be insulated, and potential B be applied 
to quadrant B; then we have, if @ be deflection which potential 
B would cause with standard charge, if quadrant A were con- 
nected to the case, and @ the observed deflection, 
0=qiA— B+ Bud 5 
o=-(A—B); 
o= — 3B 3 
sop ee Sen Ge 
ame Ps ut Be” 
In the calculated values of @ given below, 
911; 0°502, Jog = 0°548 
Qig=0°293, a=0-°200 for B, 
= (0-193 for A. 
whence 
