INTRODUCTION. 
THE present volume owes its existence to Sir J. J. Thomson’s 
suggestion that I should write an account of the present 
position of seismological investigation. 
The book is written from the point of view of Seismology 
as a branch of Physics, and particularly as it is determined by 
observatory conditions. My qualification to deal with the 
subject in this aspect rests on what is probably the unique 
experience of having set up at Eskdalemuir and having had 
under daily personal observation a Milne twin-boom seismo- 
graph, a Wiechert 80 kgm, two horizontal components astatic 
inverted pendulum seismograph, a complete Galitzin installa- 
tion of seismographs with galvanometric registration for three 
components, and an Omori seismograph for one horizontal 
component. Simultaneous records of the magnetographs and 
autographic meteorological instruments were also available for 
comparative study. 
This limited treatment of the subject is determined as 
much by conditions of available space, as by my ignorance of 
the geological side and of the practical application of earth- 
quake study to building construction which is of so much 
importance to those who live under the daily danger of the 
“earthquake”. But the limitation is no disadvantage since 
we already have Dr. Milne’s works on “Earthquakes” and 
“Seismology” (International Science Series), which deal with 
the subject in its wider aspects and with the authority of 
Milne’s unrivalled personal experience. 
The history of Seismology has been traced back to the 
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