H. L. Abbot—Transmission of Earth Waves. 179 
my reasons for believing that Mr. Mallet has not quite under- 
stood the parts of my first paper to which he has taken excep- 
tion. 
Limited space forbids any detailed explanation here of the 
method adopted for measuring the time of transmission of the 
shocks; especially as this is fully given in my printed paper, 
together with the notes of the observers in full. Suffice it to 
say that the instant of explosion and the time of arrival of the 
tremors, were electrically recorded on the same moving paper 
with extreme precision. The following table exhibits the data, 
of which only the first six observations were known to Mr. 
Mallet when he wrote his article. 
88 3 3s Peer et . 
33 Date, Observer. Cause of shock. 53 Se ; “Traperale 
ok e| ° | on. 
“ ele CCC 
miles. sees. secs. |ft. per sec. 
1 |Aug. 18, '76.'Capt. Livermore |200 Ibs. dynm. + |B} 5 + 5280 + 
2 |Sept. 24,°76.\Lieut. Young /[Hallet’s Pt. ex.| 5-134/A.| 7 +634 | 3873 + 
3| “ “ & |Tieut. Griffin “ «| g-330/ B.| 63 |72°3 | 8300 
4; “ “ ‘Lieut. Kingman] “ “ “ | 9-333) A./10°9 |23°5 | 4521 
5} “ *  |Tieut. Leach “  «& & 119-769| B. {12-7 |19°0 | 5309 
6 |Oct. 10, '76.'Lieut. Kingman |70 Ibs. powder.| 1°360| A.| 5-8 |inst.| 1240 
7 \Sept. 6, "77. Lieut. Kin Ibs. dynm.| 1°169| A.| 1°8 | 78 | 3428 
8| “ “ & ‘Lieut. Leach © & "& 1 7-169|B.| O-7% [178 |; 8814 
9 |Sept. 12, 77. Lieut. Griffin [200 lbs. dynm.| 1-340| A.| 1-05| 8:8 | 6730 
a a hed Lieut, h « «© "«& | 4-349} B.| O8L)17-1 | 8730 
1l| “ “ & |Tjieut. Griffin /70 Ibs. powder.) 1-340| A.| 1°27] 4°8 | 5559 
| Dr eee Hplt  # 1:340'B. | 0-84'15°1 | 8415 
Mr. Mallet’s results 
mat ed 
Royal Society, and unquestionabl 
were reported many 
years ago to the 
y are to be accepted as exhib- 
figures : 
in sand : Be eee Boma. 
in discontinuous and much shat- 
te (tec i AR. 
Velocity in ft. per second 
- “ “ 
ve 5 
‘in more solid granite .--. .-.-- 
in quarries at Holyhead (mean) 1320 ft. 
The extraordinary differences between these rates and those 
measured at the Hallet’s Point explosion, and the apparent dis- 
crepancies of the latter among themselves, led me to so plan 
the new observations as to throw light upon two points: Ist, 
Does a telescope of high power detect a tremor in the mercury 
in advance of the one first revealed by a lower power? 2d, Is 
“ is 
bd “ “cc 
