=< CLC 
ON SEISMOLOGICAL INVESTIGATIONS. 271 
[The remainder of this section is due to Mr. Shaw.] 
The movements of the tableare produced by anelectrically driven cam, the amplitude 
and periodicity of which can be changed at will. Its motion is recorded mechanically 
on smoked paper. The seismograph is placed upon the table, but records photo- 
graphically. Both curves are timed by the same electric circuit. The apparatus was 
tested with both simple and complex periods and in each case faithful records were 
obtained. 
Fig. 1 illustrates curves where the periods of the table and pendulum were alike 
(a condition when distortion due to synchronism is most likely to develop). Curve A 
shows a table movement of 0:13 mm. magnified 109 times. B is the corresponding 
seismogram, in which, by the Galitzin formulas, the magnification should be 187. 
W 10 
Gy td ae 
Inseri htion Milne Sha f 
STRASBOURG 149424 MARCH 382 
Fic. 1. 
Measurement of the curve shows magnifications ranging between 181 and 187, illus- 
trating not only the fidelity of the seismogram but also the close agreement between 
present practice and the formula in use. 
While referring to instrumental points of this kind, it is interesting to observe how 
two machines standardised to similar constants and fully damped do produce similar 
