Dr. C. Davison—British Earthquakes. 417 
The next Table (VII) shows how slightly the time-relations of the 
sound and shock yary throughout the sound-areas of strong earth- 
quakes. 
Tasie VII. 
wee Relative 
ee Beginning. End. Dec 
OVE Oo SiS SOUR NE ON 
67 | 30 3 | 19 | 42 | 38 | 70 | 28 
69 | 24 7 | 15 | 42.) 44 | 69 | 24 
70 | 20 | 10 | 15 | 44 | 41 | 66 | 27 
63 | 25 | 12 | 21 | 44 | 36 | 54 | 38 
Dame 
wm~ Tt 
The precedence of the shock by the sound is generally attributed 
to a greater velocity of the sound. If this were the case, however, 
the sound, with increasing distance, would be more generally heard 
before the shock and less frequently after it. There is no evidence 
whatever of such a displacement of the sound in the above Table. 
The only tendency distinctly noticeable is towards equality in the 
relative duration, and this might be expected from the gradual 
quenching of the weaker vibrations which constitute the fore-sound 
and after-sound. 
Minor SHocks. 
The series of slight shocks which oecur in Great Britain belong to 
two classes, one including those which have been confined to Glen 
Garry and the Ochil district, the other those which precede and follow 
the stronger earthquakes. 
The Glen Garry series lasted for about ten years, from 1889 to 
1899. In this interval 41 slight shocks were recorded, the majority 
occurring during the three years 1890-2, when the numbers felt 
were 11, 18, and 6 respectively. The Ochil series began in the year 
1900, and is still (1910) continuing with unabated frequency. Up to 
the end of 1909, the total number recorded is 83, 4 having occurred in 
1900, 1 in 1908, 10 in 1905, 19 in 1906, 13 in 1907, 17 in 1908, and 
18 in 1909. They vary considerably in intensity. Two, namely, those 
of September 21, 1905, and October 20, 1908, were strong within the 
epicentral district, and each disturbed an area of about a thousand 
square miles. But they should be regarded as stronger shocks than 
usual, rather than as the parents of trains of after-shocks, for the 
slight shocks which followed were not more frequent immediately 
after them than at other times. 
True accessory shocks are almost confined to the strong earthquakes 
which disturb areas of more than 5000 square miles. The total 
number of such shocks is 71, all but five of which attended the strong 
earthquakes and the Inverness earthquake of 1890, and of the majority 
15 were fore-shocks and 51 after-shocks. It is worthy of notice that, 
as regards after-shocks, there is a marked difference between simple 
and twin earthquakes. The three simple earthquakes of Inverness in 
DECADE V.—VOL. VII.—NO. IX. 27 
