STANDARDIZATION OF SEISMOGRAPHS 29 
and considerable skill is necessary. About ten experiments 
are made so as to improve the accuracy. 
The standardization of the vertical component seismo- 
graph proceeds in precisely the same manner as regards &, py’, 
and & In this case the primary period is about 13’ while & 
is of order 240 units. The quantity / of order 400 mm. is 
determined before the instrument is set up by removing the 
controlling spring, turning the instrument so that the pendulum 
may hang vertically, and observing the period of vibration. 
When in use a small correction may be made on account of 
the position of the small adjustable gravity weight. 
In the Galitzin Seismographs the indicating length is 2 A 
where A is the distance from the galvanometer to the record- 
ing drum, usually chosen to be about 100 cm. Thus if the 
theoretical adjustment has been .secured the magnification for 
periodic waves is 
Pele S87 
ml (1+) 
The expression is a maximum for #=1/3!=0'577 and the 
value of w/(1 +z”) is then 0°325. Thus the magnification is 
nil for very rapid vibrations, rises to a maximum, and then 
falls again to o for very slow vibrations. As an example, if 
i245 sees) \— 100 em, 2— 12. cm. £—do the maximum 
magnification would be 828 when T= 14 sec. 
where «= 2/p=T/T, 
