H. L. Abbot—Transmission of Earth Waves. 181 
ite usually reaches its maximum in a very small fraction of a 
second.” 
of the tremor was much less. The reason is, that the initial 
earth waves were far more violent in the latter case, when the 
torpedo lay on the bottom in thirty feet of water, than in the 
former, when the charge was only submerged five feet in water 
thirteen feet deep, and thus expended much of its energy in 
throwing a huge jet of water 330 feet into the air. s 
Thus it will be seen that these records, and the velocities 
observed on the two days, all tend to confirm the idea that a 
slow-burning explosive, like gunpowder, generates a series of 
gradually increasing tremors which, at a distance of a mile, are 
at first quite invisible with the less sensitive seismometer ; 
and are only detected by it when near their maximum inten- 
sity. If Lieut. Leach’s estimate of time for the arrival of the 
orgie wave be accepted, we have, therefore, for the first 
ile: 
’ 
( Power of 12 gives 8415 feet per second. 
p rpedo j “ce 6e “ 59 “ “ i 
(70 lbs.) Estimated mini- | o4g9 «@ «we 
er gi 
m pow ves 
Shallow torpedo; actual minimum t 1240 “« « “ 
(70 Ibs.) power gi 
by No. 6and No. 11 has been already pointed out. Fora 
power of 12, the table shows that for the first mile: 
400 Ibs. of dynamite give 8814 feet per second. 
200: 2 a one 
70“ “powder (deep) 8415 “ “  “* 
__If it be admitted also that the velocity of the wave dimin- 
ishes with its advance, all the data become accordant. Thus: 
