]yiE. I^IALLET Om THE TEANSIT-YELOCITT OE EAETHQIJAKE WAVES. 673 
through the quartz rock at the quarries in rear of the headings is marked by a pair of 
interrupted lines. 
The Map is to a scale of IJ inch to 1000 feet, but is not quite exact as to filling in 
details on land. The important distances here concerned are therefore marked in by 
figures. 
In the following Table our chief numerical results are comprised at one view. 
Table I. — ^^Yave-transit Period, Experimental Pesults. Holyhead. 
1. 
2. 
3. 
4. 
5. 
6. 
7. 
8. 
9. 
10. 
11, 
Date of 
firing heading. 
Nvimber 
of the 
heading. 
Number 
of the 
quarry. 
Weight 
of 
poirder 
exploded. 
Approxi- 
mate 
weight 
of roch 
remoTed. 
Total 
distance 
of mean 
centre of 
heading 
from 
obserrer. 
Total 
observed 
time of 
transit. 
ObserTed 
rate of 
transit 
per 
second, 
uncor- 
rected. 
First time 
correction 
for the 
seismoscope 
.+ i*! 
distance. 
Transit-rate 
with first 
correction 
(col. 9). 
No. 
1856, Not. 13 ... 
No. 46. 
No. 9. 
lbs. 
3,200 
tons. 
10,000 
feet. 
6582-93 
secs. 
7*3t6 
ft. per sec. 
896-12 
ft. per sec. 
58-248 
ft. per sec. 
954-368 
1. 
1856. Not. 13 ... 
No. 10. 
No. 3. 
2,100 
7,500 
5470-57 
5-658 
967-93 
62-915 
1030-915 
2. 
1857, Maj 16 ... 
No. 31. 
No. 9. 
2,600 
9,000 
6377-14 
6-524 
977-26 
63-522 
1040-782 
3. 
1857, Dec. 18 ... 
No. 33. 
No. 9. 
6,200 
20,000 
6403-48 
5-455 
1173-87 
76-302 
1250-172 
4. 
1860, Not. 24 ... 
No. 80. 
No. 3. 
12,000 
36,000 
5038-13 
4-161 
1210-79 
78-701 
1289-491 
5. 
1861, May 11 ... 
No. 84. 
No. 4. 
4,400 
13,000 
5228-59 
5-249 
996-11 
64-747 
1000-857 
6. 
The first result that strikes the eye at once in regarding the preceding Table is, that, 
with the exception of the experiment No. 1, all show that the transit-rate tends to 
increase in velocity uith the increased quantity of powder fired, — in other words, that the 
loss of velocity in the same rock is less, in some proportion, as the force of the originating 
impulse of the wave is greater, and its amplitude therefore greater on starting. 
This is apparent if the uncon’ected transit-rates (col. 8) be arranged in the order of 
increased w^eights of pow'der exploded, thus : 
Table II. 
Number of experiment ... 
2 
3 
1 
6 
4 
5 
Weight of powder (lbs.) ... 
2100 
2600 
3200 
4400 
6200 
12000 
Uncorrected transit-rate 1 
(feet per second) J 
967-93 
977-26 
896-12 
996-11 
1173-87 
1210-79 
Experiment No. 1 forms the only exceptional case, and the departure is not a wide one ; 
so that the result cannot be riewed as accidental, or due to any balancing of errors, but 
as the expression in so far of a fact of nature. 
Nor is it due to relative differences of different experiments in the lengths of range, 
in the quartz rock and in the slate respectively, as might be imagined ; for the experi- 
ments Nos. 2, 5, and 6 had wave-paths of about 1400 feet in quartz only, and embrace 
the lowest and the highest velocities, while Nos. I, 3, and 4 had about double this 
range or wave-path in quartz, with velocities not widely different from each other, or 
from No. 2. 
4 Y 2 
