112 rePortT—1890. 
taneous capacity can be found. The resistances R, Ry, can always be 
arranged so that the effect of the charge rushing into the air condenser 
shows itself as a shar p kick of the spot ‘of light—to the left, say—followed 
Fic..7. 
by a slower deflection in the other direction, due to the absorption charge 
soaking into the mica or paraffin. The resistance for which this sharp 
kick practically disappears is fairly definite, and from it the instantaneous 
capacity can be found, while an observation of the resulting kick due to 
the absorption enables us to calculate the increase of capacity which 
arises from that cause. This can be done in various ways. ‘The simplest, 
perhaps, is to disconnect the condensers from the circuit, and, replacing 
the mica condenser by a variable condenser of small capacity, observe the 
kick this produces in the galvanometer when charged with the same 
battery. From this the capacity to which the absorption is equivalent 
can be approximately calculated. 
Thus a condenser of about ‘1 microfarad was compared with Dr. 
Muirhead’s three condensers combined. Taking Cy, Rk, to refer to the air 
condenser, we had 
C,="009506 
Ry=898650 ohms; 
and with r,=89300 there was a slight tremor to the left and a movement 
of three divisions to the right. On changing R, by 100 ohms the change 
in the motion of the spot was marked. 
This gives for the instantaneous capacity c,;='09550; the value found 
by the commutator at frequency 64 was ‘09543 microfarad. 
To evaluate the five divisions the air condenser was disconnected and 
the mica condenser replaced by one of capacity ‘001 microfarad; the 
kick observed was 4°8 divisions, while with ‘002 microfarad it was 9 
divisions. Thus a kick of 5 divisions corresponds to about ‘0011 microfarad 
capacity. Hence the capacity of the mica condenser, including full 
effect of absorption, is ‘0966 microfarad. 
The second method, about to be described, in which the bese ation 
effect is included, gave ‘0965 microfarad. 
Let us now consider the second method. The current from a battery 
