114 REPORT—1890. 
where v is the potential of the junction of the two condensers. Should 
there be any delay in obtaining the balance, the position of v on the 
slides will vary—say to v,; then the charges on the two condensers will 
be 
Vv) 8) and (v—%) (Soto) 
respectively, where o is the apparent increase of capacity of Ss, due to 
absorption or soaking in of charge. On disconnecting the armature of s, 
from the slides and putting it to earth, the potential falls from v to 0, 
and immediately afterwards the potential of the junction of the two 
condensers becomes, say, V2, so that 
8, Vj +82 (v1) —V) =(8; +582) Ve 
Hence 
, (8; +82) —V So=(S) + 82) V2 
or 
VU; —V2 
So=S}. ——— 
V—(%—%2) 
vy and v, are known, and v, is indicated at once on an electrometer ; or 
when a galvanometer is used it can be measured quickly thus :—As soon 
as v, has been observed, break the galvanometer contact and move the 
index of the slides down to 0; then directly after bringing the armature 
of s, from the full potential of the slides to zero, close the galvanometer 
circuit and observe the throw, a, which is a measure of v2, the potential 
of the junction of the two condensers.’ 
In my own experiments, which were made after consultation with 
Dr. Muirhead, I adopted a method practically the same as his; but 
before describing it, it will be better to consider rather more the effects 
of absorption. Let us suppose, at first, that the leakage from either 
condenser is inappreciable. If there be no absorption, each condenser is 
charged to its full potential practically instantaneously ; and it does not 
matter when or in what order the keys, K,, Ky, are put down, the position 
of P on the slide is not affected. , 
Suppose now that c, shows absorption, the capacity increases with 
the time of charging. We can get the instantaneous capacity by depress- 
ing, first, the key kK, and then K,, but in this case we are troubled with 
the effect of the slow after charging as in the other method. Still the 
resistance, for which the kick due to the initial charging is zero, is, 
with the condensers I employed, fairly marked, and a value for the 
instantaneous capacity can be thus fairly accurately obtained. 
If, now, Ky be made for 1 second and then x, depressed, a different 
position will be found for rp. With this interval of charge the apparent 
‘capacity differs appreciably from its instantaneous value, and the after- 
effects of the absorption can still be observed. The same is true for 
intervals of 2, 3, or 4 seconds—the value obtained for the capacity in- 
creases, and the after-effect is still noticeable; but with the condensers 
and battery I used, if the time of charging was prolonged to 5 seconds, 
the after-effect was inappreciable, and the position of Pp on the slide, and 
hence the apparent value of the capacity, was hardly affected by further 
increasing the time of charge. In the experiments on a cable recorded 
in Dr. Muirhead’s paper already referred to, the absorption effects con- 
tinue much longer. In the observations recorded below, then, unless the 
