284 Proceedings of the Royal Society of Edinburgh. [Sess. 
the shock consists of two parts, separated by an interval of about two 
seconds, but there is no reason whatever for regarding such as twin 
earthquakes. 
Sound- Phenomena . — In the earthquakes of the first class, the sound 
was heard by 88 per cent, of the observers ; in those of the second class 
by 92 per cent. ; and in those of the third class by 98 per cent. The in- 
creasing percentage as the intensity lessens is due to the fact that the 
sound is by far the more prominent feature in the slighter earthquakes. 
The variation in the nature of the sound in the three classes of 
earthquakes is shown in Table II, in which the figures represent per- 
centages for each class of earthquake to the different types of sound 
(Davison scale). 
Table II. 
Waggons 
passing. 
Thunder. 
Wind. 
Loads 
of Stones 
falling. 
Fall of 
a Heavy 
Body. 
Explo- 
sions. 
Miscel- 
laneous. 
Class i . 
28 
19 
5 
7 
24 
15 
2 
Class ii . 
21 
11 
11 
7 
30 
14 
6 
Class iff . 
9 
13 
5 
5 
25 
42 
1 
Omitting- the miscellaneous sounds in the last column, the first three 
types are of long, and the others of short, duration. In Class i, 47 per 
cent, of the comparisons are of short duration ; in Class ii, 54 per cent. ; 
and in Class iff, 73 per cent. 
In Table III, the time-relations of the beginning and end of the 
sound and shock are given, the figures in the columns headed p, c, 
and /, respectively, representing the percentage for each class in which 
the epoch of the sound preceded, coincided with, or followed, the corre- 
sponding epoch of the shock. Under the heading “relative duration,” 
the figures in the columns headed g, e, and l , respectively, represent the 
percentages for each class in which the duration of the sound was greater 
than, equal to, or less than, that of the shock. 
Table III. 
Beginning. 
End. 
Relative Duration. 
V • 
c. 
/• 
p. 
c. 
/• 
9- 
e. 
l. 
Class i 
50 
42 
8 
19 
51 
30 
41 
47 
12 
Class ii 
38 
50 
12 
19 
53 
28 
36 
61 
3 
Class iff . 
37 
46 
17 
9 
51 
40 
29 
67 
4 
