416 Dr. C. Davison—British Earthquakes. 
TABLE V. 
Thus, as the distance from the origin increases, there is a steady 
diminution in the references to types 2, 4, and 6, an increase in 
those to type 8, and on the whole an increase in those to type 1.' 
Omitting type 7, the percentage of references to the types of long 
duration (1 to 8) for successive zones are 76, 81, 86, 88, and 94, 
implying, not that the duration of the sound increases, but that 
the sound becomes smoother and more monotonous in the outer 
zones. 
Occasionally, the sound is heard before the shock and becomes 
inaudible as soon as the first vibrations are felt. With a very few 
exceptions, however, the sound, when heard at all, accompanies the 
shock, though it is heard by many observers both before and after 
the shock. The time-relations of the principal epochs of the sound 
and shock are given in Table VI, in which the figures in the columns 
headed p, e, and f denote the number of records per cent. in which 
each epoch of the sound preceded, coincided with, or followed the 
corresponding epoch of the shock; those in the columns headed g, 
e, and Z denote the number of records per cent. in which the duration 
of the sound was greater than, equal to, or less than that of the 
shock. 
Taste VI. 
eto Epoch of Relative 
Earthquakes. pee. one: Max. Int. Duration. 
aes he | 
ag Choa leeefiam||, 622 Ngee ye | c | SF ianeg, e 1 
Strong . | 66 | 25 | 9 | 15 | 40 | 45 | 22 | 68 | 10 | 68 | 27 | 5 
Moderate . . | 66 | 29) 5 | 12 | 48) 45 | 24 | 738 | 3B) 75 | 28 | 2 
Slight. - . | 59 | 84 | 7 | 14] 47 | 40 | 83 | 67 |... | 68 | 41) 2 
This table shows that there is a close resemblance, as regards 
time-relations, between all three classes of earthquakes. Roughly 
speaking, two out of every three observers who hear the sound at all 
hear the fore-sound, two out of every five hear the after-sound, while 
to two out of every three the sound is loudest at the instant when the 
shock is strongest. 
1 The slight decrease in the two outer zones is probably due to the comparative 
uniformity in the intensity of the sound at great distances. 
