1897-98.] Note on Indian Earthquake, 12th June 1897. 17 
It will be seen that the beginning of the seismic disturbance, as 
recorded by this instrument, shows that it was somewhat sudden 
and abrupt, and the rise to the maximum after the commencement 
was within three minutes to four minutes, while the falling off, as 
shown by the clear trace, appears to have taken place gradually and 
steadily till normal conditions were reached. From the very 
regular trace it appears that the time of vibration of the magnet 
must bear a certain relation to the period of disturbance, the exact 
time of vibration being some even sub-multiple of the period, 
otherwise the regularity of the vibrations would be disturbed by 
1 interference * 
The average displacement of the declination east or west during 
the fourth wave, which is well defined, would equal that due to a 
change of '00034 C.G-.S. units, in terms of force. 
If by producing the curves on each side we get the probable 
amplitude of the most intense wave where the two lines meet, the 
average displacement appears to be '1 5 inch, equal to *00051 C.G.S. 
units, in terms of force ; and this shows that the second wave was 
the most intense. 
The magnetic disturbance of the kind registered on the trace 
appears suggestive of some kind of fluid action or of some kind of 
undulatory action. The phenomenon appears as if due to an 
agitation of a fluid endowed with magnetic properties in some 
large subterranean cavity, upon which the indications of the 
Colaba magnets at least partly depended, and as if the seismic 
convulsions produced waves in this fluid which, approaching the 
instruments at Colaba and passing away from them, caused the alter- 
nate fall and rise of declination, these waves following each other 
regularly at an interval of two minutes. And any such wave must 
travel east to west at right angles to the declination magnet to 
affect it with maximum effect —passage of such waves due north to 
south having no influence on the declination. 
The trace here (fig. 2) shows the disturbance in the horizontal 
intensity, which appears to have commenced early, about 2 \ minutes 
after four, while the instrument shows that the disturbance did not 
end before 36 minutes past four. The sudden displacement of the 
curve at the beginning shows that the vibrations must have been 
performed about a displaced zero above the curve, showing increased 
YOL. XXII. 24/1/98 B 
