STANDARDIZATION OF SETSMOGRAPHAS 7 
The quantities c, and ~, are determined for the galvano- 
meter in the usual way. The period is about 24‘ while ¢, turns 
out to be a very small quantity of order 0:0005. 
When the circuit is closed we see that e, increases as R 
diminishes and thus the condition of true aperiodicity «=, 
can be secured by suitable choice of R. The value is deter- 
mined by experiment thus: Different values of R are intro- 
duced and the corresponding values of e, determined. In this 
way cis found and is a quantity of order 6 units. We may 
then calculate the value of R required to make ¢, = ,, and find 
it to be about 25 ohms, Thegalvanometer resistance is about 
4 ohms and thus the remainder of the circuit must be made up 
to the required value. When this is done the galvanometer 
is assumed to be aperiodic (€,=%,) and to remain so as the 
quantities involved are not subject to changes that have any 
appreciable effect. 
Having granted the desirability of great damping, the 
passage to the limit of aperiodicity seems obvious as it simpli- 
fies the relation between the quantities. Thus the ideal is to 
have the pendulum and galvanometer truly aperiodic and to 
have the same primary period in the absence of damping, i.e. 
€=¢€=%=%n,. Assuming then that ¢,=, we proceed by trial 
to make e=”=A,, or yw? =O, and it is easy to get quite near it. 
The adjustment would in fact not be considered good if p? rose 
to O'I or if the primary periods differed by more than a few 
tenths of a second. The pendulum does, however, undergo 
small secular changes, and we have now to explain how Galitzin 
determines how far x differs from %,, and yp? from 0, and also the 
value of & the transference factor of order about forty units. 
To simplify matters, suppose the ideal condition secured 
and that a small impulse is given to the pendulum. Then 
0 = 12,60 ,e~ 
so that @,, is the maximum value of 6. 
The corresponding motion of the galvanometer needle is 
given by 
p= —knje 0, e~ @ ~ ee) 
24258 
so that ¢= p=0 when ¢=0, 
