60 REPORTS ON THE STATE OF SCIENCE.—1913. 
South motion. A good illustration of this is found in all the registers 
from Eskdalemuir. In 1910 the East-West and North-South pendulums 
indicated a maximum 12 times simultaneously; the East-West 
pendulums, however, had a maximum 41 times in advance of and 
six times later than the North-South instrument. When the natural 
period of the pendulums was not identical they did not vary from each 
other more than one second, the period for the East-West recording 
instrument being 18 seconds whilst that for the North-South was 
17 seconds. This slight difference in sensibility in the two instru- 
ments does not, however, explain why the East-West component, 
although usually giving earlier records, should occasionally give them 
simultaneously with and sometimes after the North-South instrument. 
At San Fernando in South Spain there is a pair of Milne pendulums 
mounted to record East-West and North-South motion. The natural 
period of the first of these instruments is 16 secs., and 1 mm. deflection 
of the outer end of the boom corresponds to a tilt of 0°43. The 
period of the second is 20 seconds, and 1 mm. deflection of the outer 
end of the boom is equivalent to a tilt of 0/-25. As regards the 
displacement produced by tilting, the first of these instruments, which 
records East-West motion, has only half the sensitiveness of the other. 
Notwithstanding this, in 1910 the maximum for Hast-West motion 
was obtained before North-South motion 17 times. Twice both 
pendulums recorded maxima simultaneously, while the very sensitive 
North-South instrument showed maxima 26 times earlier than the 
East-West boom. 
IX. Disturbances only recorded at Two or Three Widely Separated 
Stations. 
In the British Association Report for 1858, p. 55, Mallet refers 
to a number of shocks which had been felt simultaneously, or nearly 
so, at two distant places. The most remarkable pair are shocks noted 
at Okhotsk and Quito, places which are nearly antipodal to each 
other. As these coincidences cannot be assured within several hours, 
Mallet agrees with Mylne? that ‘the probability of anything more 
than mere coincidence is extremely slight.’ 
In the British Association Reports, 1908, p. 64, and 1909, p. 51, 
I called attention to 148 small disturbances which had been noted in 
Jamaica. Fifty-one of these were undoubtedly recorded 43 minutes 
later at several stations in Great Britain. They were not, however, 
noted in Europe. This absence of records across the Channel was 
attributed to a want of sensibility in the seismographs which were 
there employed. Although we know that the seismograph recording 
photographically will pick up very small movements which may or 
may not be visible on the record received on smoked paper, whether 
a microseism shall or shall not be noted apparently depends not 
only on the sensibility of the recording instrument but on other 
conditions not yet defined. 
As illustrative of this I called attention to the fact that from 
time to time Batavia and Cairo have recorded the same earthquake, 
which, however, has not been recorded at stations lying between 
‘See ‘ Brit. Earthquakes,’ Edin. Phil. Journ., vol. 31. 
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