CHAP DE RIGIN: 
STANDARDIZATION OF SEISMOGRAPHS INCLUDING THEORY OF 
MECHANICAL AND ELECTROMAGNETIC REGISTRATION. 
IN order that the study of seismograms should contribute 
in real measure to a knowledge of geophysics, it is essential 
that the results obtained should be expressed in absolute 
measure. When we remember that we have to compare 
records obtained at different stations with instruments, it may 
be, of the same or even of different types, the necessity for stand- 
ardization becomes evident. Not only so, but since any indi- 
vidual instrument undergoes secular change and _ requires 
readjustment from time to time, it must be possible to deter- 
mine the constants of the instrument zz sztu at suitable 
intervals. 
In the first instance it is, however, important that each 
instrument should be tested in order to ascertain whether it 
conforms to the fundamental equation supposed to represent 
its motion. This can only be done on a properly equipped 
experimental table by some central recognized authority, 
which would then issue with the instrument a certificate giving 
any data of importance. 
We shall consider how the constants are to be obtained at 
the station for the three well-known types, Milne, Wiechert, 
and Galitzin. 
The latest form of Milne’s twin-boom Seismograph readily 
lends itself to the determination of the quantities e and ” on 
the photographic sheet itself, a point of great practical con- 
venience. If the end of the boom is given a suitable initial 
displacement and then left to itself, excellent decay curves are 
obtained. The diagram (fig. 8) is an exact reproduction of 
an actual curve obtained in this way. 
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