1907 - 8 .] Professor C. G. Knott on Seismic Radiations. 
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XII. — Seismic Radiations. By Professor C. G. Knott, D.Sc. 
(Read December 2, 1907 ; and January 20, 1908.) 
When a large earthquake occurs in any part of the earth, its tremors 
can be recorded on suitable instruments all over the surface of the globe. 
These instruments are of various types, the most familiar being the 
horizontal pendulum, the evolution of which we owe to the labours of a 
small band of enthusiasts who were engaged by the Japanese Government 
in the late seventies and early eighties to teach the students of Japan the 
scientific methods of the West. The most conspicuous of these is un- 
doubtedly Professor John Milne, who in his seismological laboratory 
established in the Isle of Wight continues to study the mysterious move- 
ments of the earth. Prompted by him, the British Association has installed 
some fifty instruments in various parts of the world ; and from the 
accumulating records furnished by these instruments, Milne pursues his 
seismological studies. In addition to these fifty British Association 
stations, there have grown up in recent years many seismological labora- 
tories in Europe, Asia, and America ; and the data supplied from all these 
sources place us in a much better position than ever before to draw sure 
conclusions from the character of the records. 
In 1898 I drew a rough sketch of the probable form of wave-fronts and 
rays of seismic disturbance, basing my calculations upon the early results 
obtained by Milne as to the times of transit of the different types of motion 
which characterise the distant earthquake record. This was published as 
part of the Seismological Committee’s Report to the British Association in 
1899. A little earlier, Rudzki * and V. KOvesligethy f had independently 
worked out some brachistochronic problems suggested by the earthquake 
phenomena ; but their mathematical assumptions were made so as to get 
a soluble case, and had no dynamical basis in harmony with known seismo- 
logical facts. 
In a second paper published in 1905, V. Kovesligethy f works out his 
original theory more fully, and shows how it may be harmonised with 
certain of these facts. But his fundamental assumption that the speed of 
propagation of the seismic waves through the earth diminishes as the depth 
* Beitrage zur Geophysik , iii., 1898. 
t Mathem. u. Naturw. Berichte aus Ungarn , xiii., 1897 ; xxiii., 1905. 
