xii INTRODUCTION 
measured by the standard of modern experimental physics in 
the laboratory. 
He was led to adopt electromagnetic damping up to the 
limit of aperiodicity and to introduce electromagnetic regis- 
tration to get increased magnification. Each point of con- 
struction or of theory was submitted to the most rigorous 
tests in the physical laboratory until success was attained, and 
the observatory of Pulkowa started continuous recording and 
publication of observations on I January, 1912. 
His separate memoirs have appeared in the “C.R. of the 
Imperial Academy of Sciences, St. Petersburg,” and the results 
are embodied in his book published last year (“‘ Lectures on 
Seismometry”). The whole investigation is a most instruc- 
tive and masterly application of physical principles to obser- 
vational seismometry. 
Perhaps the most striking result attained by Galitzin is a 
complete experimental proof that his instruments determine 
not only the distance of the epicentre, but also the azimuth 
from the observing station, so that it is now possible from 
observations at a single station to determine the epicentre 
within the limits that must be assigned to the epicentral 
region itself. 
Seismographs reveal the existence of earth movements 
other than those due to earthquakes. Chief of these are the 
movements known as microseisms and earth-tides. Seis- 
mology is thus brought into intimate connexion with Astron- 
omy and Geodesy. 
It may truly be claimed that during the close of the 
nineteenth and the beginning of the twentieth century seis- 
mologists, among whom the names of Milne, Wiechert and 
Galitzin stand pre-eminent, have succeeded in dragging the 
study of earthquakes from the region of ignorance and super- 
stition and in making it a quantitative science proceeding on 
the principles of physical philosophy. 
