ON STANDARDS FOR USE IN ELECTRICAL MEASUREMENTS. 115 
contrary is stated, the key k, was held down for 5 seconds, and then, x, 
being depressed, the position of p determined, for which the galvanometer 
remained unaffected. The value of the capacity deduced then is the full 
capacity for the potential to which the condenser is charged. It is of 
course possible, though further experiments would be wanted to prove it, 
that the full effect of absorption is not merely to increase by a definite 
amount, independent of the potential, the apparent instantaneous capacity, 
but that the increase may depend on the potential to which in each case 
_ the condenser is being charged. It will of course depend on the purposes 
for which the condenser is to be used whether the instantaneous capacity 
or the full capacity is required, and it probably will be best, when issuing 
certificates, to state both the instantaneous capacity and the maximum 
increase due to absorption—mentioning at the same time the difference 
of potential used in the experiments for determining this correction, and 
also the time of charging in which this maximum increase is practically 
attained. 
The method I employed in determining the correction due to absorp- 
tion was the following:—Suppose the plates, 4), A), to be at potential 
zero and uncharged. Make the battery key, Ks, and after keeping it 
made for some little time break it again. It there be no absorption A, 
and A, will still be at zero potential and uncharged; but let there be 
absorption in one of the two, A,, and let B, be the positive pole of the 
battery, then, while the battery is on, negative electricity is being 
absorbed by the dielectric near A,, and positive electricity is left free over 
the plates, A), Ao, and the wires connecting them. When the battery is 
broken the negative electricity begins to soak out, but the process takes 
time. Hence, if immediately on breaking the battery key, kK, the 
galvanometer key, K,, is made for an instant, there is a throw of the 
galvanometer needle indicating the passage to the earth of the positive 
set free by the absorption. If, after a time, the galvanometer key be 
again depressed, there is an equal throw in the opposite direction, caused 
by the passage of the negative electricity which has again soaked out of 
the condenser. The required correction is obtained from either of these 
For, let 7 be the current between B, and B, ; let c, be the instantaneous 
capacity of the one condenser and oc, of the other; and let Q be the 
quantity of electricity absorbed. Then the quantity of negative elec- 
tricity on the plate A, is c, R, 7+, and the quantity of positive electricity 
on the plate A, is C, R, 7,if we assume the potential of these plates to be 
still zero. 
Therefore, 
C; Ry t+Q=Cy Ro t 
eee ae 
Co By Og Ri 2 
hen, neglecting the battery resistance, if n be the E.M.F. of the battery, 
; E 
a 
Ri +R 
Se) rk Pad Gs 
Sdyee Ry Cy te Ry 
