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of Edinburgh, Session 1880-81. 
Duke of Argyll; the Rev. Dr Robinson of Armagh; Mr William Philip, 
resident engineer, Londonderry ; Capt. Graham, steamer “ Pharos ” ; 
Mr David Gordon of Bathgate ; and Mr R. L. Mackintosh, Inverness. 
I may observe that this earthquake occurred in the month of 
November, during a wet and stormy period, the average rainfall for 
the month at the different places of observation being 4 A inches, 
which wet period had been preceded by an unusually dry summer 
and spring ; that it was accompanied by a widespread thunder storm, 
but no sudden change of barometer or thermometer; that the 
average height of the barometer at the lighthouse stations was, at 
9 a. m. , 29’4 inches ; and at 9 p.m. 29 ’5 inches; and that the average 
temperature at 9 a.m. was 50° P. and at 9 p.m. 48° F. 
The area over wdiich it was felt from Butt of Lewis in the 
Hebrides to Armagh in Ireland, and from Barrahead in the Hebrides 
to Blair Atholl, amounted to at least 19,000 square geographical 
miles, though to what additional extent it may have been propagated 
into the Atlantic it is impossible to say. 
The effects of this earthquake, as reported by the lightkeepers, 
show that it was a rather sharp shock, but fortunately that no 
damage was done, due no doubt to the massive structures of all our 
exposed lighthouse towers, and, judging generally from the reports 
of the shock, the undulation seems to have been of an “ up and 
down ” character like a wave of the sea. 
The “breadth” of the undulation of 1839, which emanated from 
Comrie, and which is described by Mr David Milne-Home in an 
article in the “Edinburgh Philosophical Journal” for 1843, was 
calculated by him to have been about 20 feet, but the wave of the 
earthquake now under consideration must have very much exceeded 
the Comrie one in breadth, for a wave 20 feet broad, travelling with 
a velocity of 568 feet per second (which will be shown afterwards 
to have been the average velocity of transit of the wave of the earth- 
quake of 1880) would pass a point on the earth’s surface in J-g-th of 
a second, which evidently is too short a time to produce the effects 
observed by the lightkeepers; but, calculating the breadth of this wave 
from the minimum time its effects were felt, which was two seconds, 
and from its average velocity of transit it would appear that the 
breadth of the wave was fully 1100 feet, which I think is a more 
probable breadth than 20 feet. 
