382 DR. CHARLES DAVISON ON THE [Aug. 1902, 
associated with a traction-engine passing close at hand. Both noise 
and vibration ceased, and almost immediately there followed two or 
three heaves like a slight movement in a boat. 
A berdeen.—The shock consisted of two parts, the first a tremble, 
followed, after an interval of a few seconds, by a swinging move- 
ment of longer duration than the tremble. 
Similar descriptions are given by observers in other parts of the 
disturbed area. If we divide the whole area into four quadrants 
by lines drawn through the epicentre parallel to the axes of the 
isoseismal 8, such records come, in the eastern quadrant, from 
_ Aberdeen, Aberlour, Dinnet, Duffus, Dyke, Forres, Huntly, Inver- 
ness, Monyruy, and Rothie-Norman: in the southern quadrant, 
from Aberfeldy, Blairgowrie, Dunbar, and Rothiemurchus: in the 
western quadrant, from Lochcarron: and along the line between 
the eastern and southern quadrants (that is, on the minor axis of 
the isoseismals), from Dalarossie and Montrose. Throughout the 
disturbed area, the shock thus consisted of two distinct parts, the 
second being of greater duration and intensity than the first, and 
consisting of vibrations of longer period. Near the epicentre 
there was no interval between the two parts; but, at a distance, 
the intermediate tremors were imperceptible, and the parts were 
separated by an interval of rest and quiet lasting 2 or 3 seconds.’ 
It follows that the two series of vibrations were produced by two 
distinct impulses, the stronger impulse succeeding the other after an 
interval of a few seconds. It is possible that the corresponding foci 
were nearly or quite detached, as in the twin earthquakes of Hereford 
in 1896 and Leicester in 1893; but it is more probable, I think, 
that the focus of the earlier impulse was overlapped by, or included 
within, that of the second. 
Sound-phenomena.—Outside the isoseismal 5, there are but 
few records of the earthquake-sound ; it was heard faintly, however, 
at Skelmorlie (in Ayrshire), Belsyde (near Linlithgow), and Gullane 
(near North Berwick). ‘Towards the north, it was not observed 
beyond Wick and Watten (in Caithness). The extent of the sound- 
area must therefore have been about 27,000 square miles. 
Throughout the whole disturbed area, 84 per cent. of the observers 
who describe the earthquake heard the accompanying sound. The 
percentage varies in different counties, from 93 in Inverness-shire 
to 77 in the counties of Perth and Aberdeen. In more distant 
regions, the records are too few to allow of the percentage of audi- 
bility being calculated; and the scarcity of observations in all but 
the south-eastern quadrant prevents, of course, the construction of 
isacoustic lines. 
1 According to 22 observers, who were awake when the earthquake began, 
there was only one series of vibrations, the places where they were situated 
being often close to those where the double series was observed. The duration 
of the shock-is recorded by 13 of these observers, and their estimates give a 
mean duration of 2°8 seconds. As the average duration of the shock (according 
to 59 observers who were awake) was 4°7 seconds, it is therefore probable that 
these observers noticed only the second and more powerful series of vibrations. 
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