60 REPORTS ON THE STATE OF SCIENCE.—1914. 
a Galitzin installation must always require a greater measure of ~ 
skilled attention to run it successfully than is the case with the 
simpler types of instruments. 
It is difficult to estimate what is the minimum of mathematical 
and physical knowledge that must be possessed by an assistant in order 
to maintain successfully a Galitzin installation. A working know- 
ledge of algebra is essential, and probably with this as a basis an 
intelligent operator could learn the rest of the routine with the aid 
of computing-forms. But without a knowledge of higher mathematics, 
and particularly elementary differential equations, it is impossible to 
understand the meaning of the formule by which the constants are 
determined. 
Results obtainable.—The Milne type of instrument is very sensitive 
as a mere seismoscope. With the exception of very faint movements 
indeed, some record of a distant quake can always be obtained by it; 
this is due to the absence of damping and almost entire absence of 
solid friction; by altering the period of oscillation of the boom 
it can be made particularly sensitive to any wave-period desired. 
The instrument at Eskdalemuir Observatory has at present a period 
of about eighteen seconds, and this corresponds approximately 
with the wave periods from very faint and remote shocks. For 
waves of this type the Milne instrument leaves some record of 
almost any earthquake that affects the Galitzin instrument; but 
whereas the latter gives a trace that approximately follows the actual 
movements of the ground, the trace from the former has little re- 
semblance to it. Maximum movements on the Milne record may 
or may not coincide with the maximum movements of the ground: 
it depends on the type of the earth movements and on the period of 
the pendulum. By damping slightly, a more faithful record can be 
obtained, and by making the pendulum actually dead beat a moderately 
close agreement will prevail between the actual earth movements and 
those worked out from the record. This can be established theoreti- 
cally, but Prince Galitzin has also conducted experiments which show 
that theory and practice are in close agreement. See Professor C. G. 
Knott’s book on ‘ The Physics of Earthquake Phenomena,’ chapter 5, 
Unfortunately the reduction in the scale of the record which accom- 
panies damping renders the Milne pendulum very insensitive when 
damped. For some months an oil damper has been fitted to one of the 
Milne pendulums at Eskdalemuir; the ratio of successive elongations 
is approximately 2:4. The results obtained are disappointing for the 
reason given above. 
If any satisfactory means could be found of increasing the magnifi- 
cation optically even by a moderate amount, the damped Milne 
pendulum should be capable of yielding good results, and the greater 
simplicity of standardisation should be another point in its favour. 
Turning to the Galitzin type of machine, as an instrument of 
precision it may safely be said to be ahead of all others. The inter- 
pretation of its records is not a very simple matter, but by those 
prepared to spend the time a vast amount of information can be 
