SEISMOLOGICAL INVESTIGATIONS. 211 
(1921, March 17), were still continuing. By an odd coincidence a letter was 
received from Mr. A. Pearse Jenkin, F.R.Met.S. (of Redruth, Cornwall), sug- 
gesting, from an independent standpoint, a connection between earthquakes and 
barometer changes. He draws attention to p. 226 of Symons’s ‘ Meteorological 
Magazine’ for 1906 (vol. 41), where there are some notes by Mr. W. Gaw on 
the Chili earthquake. 
(1) The third and second days previous to the great shocks were ‘ charac- 
terised by a high barometer, accompanied with rain; abnormal conditions here. 
(2) The day preceding the first seismic movement was marked by a sudden fall 
of about half an inch of barometric pressure in a comparatively short period of 
time.’ 
Mr. Jenkin’s view is that ‘at some spot on the earth there exists, from 
some exceptional cause, an area of deficiency of mass in the earth’s crust, and 
there is, according to the theory of isostasy, an endeavoar to fill up the deficient 
area and so restore the balance. The interior of the earth, being viscid, 
responds but slowly, but the atmosphere, subject to the same laws but more fluid, 
does its part in attempting to restore the balance more rapidly.’ He does not 
make his mechanism entirely clear, but neither is the mechanism of isostasy 
yet fully understood. 
Location of the Epicentre: Early Uncertainties. 
It is perhaps well to put on record the uncertainties which affected the 
localisation of this great earthquake for some days. A single completely 
equipped station, such as Eskdalemuir, can assign the locality of an epicentre 
from its own records; but unfortunately the Eskdalemuir machines were out 
of action on December 16. Other English stations have as yet only partial 
equipment: taking them in combination, they could assign two alternative 
localities, one to the East and one to the West. News from America that 
the epicentre was only 3,000 miles from them pointed to the Western alterna- 
tive, but it was very difficult to fulfil all the conditions. The direct evidence 
of the seismographs put the epicentre where a disaster of such magnitude would 
be independently recognised; it was necessary to !ook for a possible centre, 
not too far from that directly indicated, where a big earthquake might occur 
without revealing itself by telegraph to the civilised world—such as the Alaskan 
Coast, for instance. But the receipt of news from China made it clear that 
the American stations had been deceived by the magnitude of the disturbance 
into thinking it close at hand, when it was in reality far away. 
A few Details for December 16. 
The earthquake of December 16 was so exceptional that a few figures may 
be given here. The adopted epicentre (calculated before Mr. Mann’s map 
was received) is 105%.5 E., 35°.5 N., and the time at origin T)>—12" 5™ 46*, 
A Azim. Obsd.P O—C Obsd. S. o—C 
Station i ix mip! 8. m. 8s. 8. 
Calcutta ‘ . 19:8 236 10 30 + 5 14 12 +5 
Kodaikanal . - oosg  2a0 18> “6 — 1 — — 
Vienna ‘ a 6358 O12 16 19 — 4 24 58 +] 
Padova ; e (6dED 311 16 49 + 2 — = 
Dyce . ; . 692, 327 16 58 0 25 58 nA. 
West Bromwich . 71:8 323 17 #14 —l 26 29 —5 
Oxford : . 71-9 322 Link 0 26 31 —4 
Riverview. 0 81-5 onl 43 18 15 +2 28 28 + 2 
Sydney ’ w981:5 948 18 12 — 1 28 30 +4 
Honolulu. +1 82-8 70 18 24 aE 3) 28 42 4 | 
San Fernando / 841, 812 18 27 —2 28 36 —19 
Saskatoon . . 88-0 21 18 39 =12 29 19 —19 
Ottawa F . 99-1 1 19 27 —25 30 «6 —87 
La Paz . - 1601 — 25 58 ~- 40 10 — 
