THE TIME AND ORIGIN OF THE SHOCK, 5 
is probably due therefore to slight derangements by the preliminary shocks, and to the in- 
stantaneous positions of the pendulums, which enabled one to be hung fast a second or more 
before the other; but I think the mean time here adopted js likely to be correct within 1 
second. 
Mr. J. D. Maddrill, in charge of seismographs and earthquake reports at Lick Observa- 
tory, Mount Hamilton, reports the beginning of the shock there, as the result of several 
observations, as 5° 12™ 12°. Mr. R. G. Aitken timed the heavy shock at 5" 12™ 45%, which 
corresponds exactly with the starting of the Ewing three-component seismograph. 
On comparing these accounts, we notice that Professor See alone, probably on account 
of his unusually favorable situation, observed a very slight movement between 5° 11™ 
and 5° 12™, and soon afterwards the violent shocks began, which correspond to the 
~ beginning noticed by Professor Davidson, Professor McAdie, Dr. Albrecht, and the Lick 
observers; this part of the disturbance was very strong, tho much lighter than the 
very violent shocks which occurred later. We shall refer to it as the beginning of the 
shock, looking upon the earlier, extremely slight movement observed by Professor See as a 
preliminary movement. Dr. Albrecht reports the heaviest shock at 30 or 40 seconds 
after the beginning; Mr. Aitken is corroborated by the starting of the seismograph at 
Lick Observatory in putting the heavy shock at 5° 12™ 45%, 7.e., 33 seconds after the 
beginning; and the most reliable clocks that were stopt agree in indicating a similar 
interval between the beginning and the shock that stopt them. As pointed out by Prof. 
C. F. Marvin,’ the evidence is convincing that the clocks in general were stopt by the 
violent shock, which occurred about a half minute after the beginning, and was alone 
strong enough to affect seismographs at distant observatories. 
THE BEGINNING OF THE SHOCK, 
The majority of the reports as to the time of the beginning of the shock are only roughly 
approximate, but we fortunately have four very reliable observations, all of which are 
given by astronomers, who are accustomed to accurate estimates of small intervals of 
time. 
First, San Francisco: Prof. George Davidson gives the time as 5° 12™ 00° + 2 seconds, 
Pacific Standard Time, which is 8 hours slow of Greenwich Mean Time. Mr. Van Ordin, 
who had a stop-watch, gives the time as 5" 12™ 10°; his watch was set two days before 
the earthquake and his time is not so reliable as that of Professor Davidson. Professor 
McAdie’s time may be looked upon as confirming Professor Davidson’s; all the reliable 
observations, as well as the reliable stopt clocks, make it absolutely certain that the 
shock began about 5° 12™ and we must assume that Professor McAdie, suddenly awak- 
ened by a strong earthquake, made an error in reading the minute-hand of his watch, an 
error which is very easy to make; or that he applied the approximate correction and wrote 
down the corrected time. We shall accept Professor Davidson’s time as the most accurate 
obtainable for San Francisco. 
Second, Students’ Observatory, Berkeley: Dr. S. Albrecht, 55 12™ 06°. 
Third, Lick Observatory, Mount Hamilton: The result of the observations of several 
astronomers, 55 12™ 12°. 
Fourth, International Latitude Station, Ukiah: Prof. S. M. Townley, 5° 12™ 17%. 
Professor Townley had been at work very late the previous night and was sleeping soundly 
when he was awakened by the earthquake. He immediately arose and went to the 
window and took the time of his watch, which when corrected became 5° 12™ 32°. 
Professor Townley estimates that 10 seconds may have elapsed from his first awakening 
and his reading of the watch, and that it may have taken 5 seconds for the disturbances 


1 Professor Marvin’s Preliminary Report to the Commission on the Stopt Clocks has been drawn upon 
freely in this discussion. 
