40 RTl'AnT : THE SRIMANGAL EARTHQUAKE OF STH JULY 1918. 
than the s cond preliminary ; the damping out of the oscillations of 
short period has not been powerful enough to bring the long waves into 
prominence. In the second place the tlistance of 520 miles is too short 
to give a i origin in Assam, and if we treat the large oscillations beginning 
at 15 hours 59 minutes 5 seconds as the second preliminary vibrations, 
the distance of origin is about 1,020 miles, which is of the right order of 
magnitude. Lastly the second ]iieliminai-ies are transverse oscillations and 
we should expect them to be more marked on the iiistniinpiit registering 
north-south movements than on that registering east-we^(. This actually 
happened, fo/ the former beat the steps so violently that it did about S 
complete oscillations a minute while the latter did about 2i." 
I offer, with some diffidence, a different interpretation of the 
Simla seismogram. The natural period of the instrument seems to 
have been long and the first two series of oscillations are accom- 
panied by the natural swing of the pendulum ; also the instrument 
was registering badly against the time marks. 
I would suggest that the three series of oscillations recorded on 
the (Simla) seismogram are P., S., and the long waves. If the 
second series of oscillations is taken to be the second preliminary 
vibrations, and the large oscillations to be the long waves, then the 
measurement of the seismogram gives S — P=2^ seconds which gives a 
distance of origin of 15°, or approximately 1,050 miles, which is of 
the right order of magnitude. It will be seen below that the read- 
ings fit in with the readings of other observatories if they are regarded 
as preliminary, second preliminary vibrations, and long waves, 
rather than as suggested by Dr. Walker and this has led me to offer 
a different interpretation of the seismogram to that suggested by 
him. Plate 8 shows a reproduction of the Simla seismogram. 
Dehra Dun. 
The seismograph in the laboratory of the Survey of India at 
Dehra Dun shows a ])rccisely similar record to the Simla seismogram. 
The first preliminary tremors are registered at 15 hours 54 
minutes 15 seconds. Stronger oscillations come in at 15 houre 
56 minutes 22 seconds and large oscillations at 15 hours 58 minutes 
45 seconds. These large oscillations persist for about 2|- minutes 
and then begin to diminish, but at 16 hours 4 minutes become 
equally strong again, last for just ovei 2 minutes and then gradually 
diminish. 
