182 H. L. Abbot—Transmission of Earth Waves. 
200 lbs. of dynamite give for 1 mile, 8730 ft. per second. 
oe 6s oc “ “ “ce 5 “c ¢ oe 6 ce 
50.000 “* *& “ oe “cc 8 “6 8300 “be oe 
% en 2 “cc se “cc 134 (74 5300 OG “cs 
In fine, I believe that the following general conclusions are 
suggested by these measurements: Ist, igh magnifying 
4th, 
are complex, consisting of many short waves first increasing 
and then decreasing in amplitude; and, with a detonating explo- 
sive, the interval between the first wave and the maximum wave, 
at any station, is shorter than with a slow-burning explosive. 
summary of the objections suggested by Mr. Mallet to 
the Willet’s Point observations will now be given ; although, 
in the new light thrown upon the subject by these subsequent 
measurements, perhaps he might not desire to press them. __ 
Mr. Mallet considers that the explosion at Hallet’s Point 
furnished data ill suited to determine the delicate physical 
problem of the rate of progression of a wave of disturbance 
through the earth’s crust, for the reason that the initial impulse 
was due to the combined effect of many small charges, and not 
of one single mass of dynamite; hence, as he states : : 
‘\I conceive it, therefore, impossible with sufficient exacti- 
tude to assign the instant at which the wave of shock sta 
in this instance; and to assume the appearance of disturbed 
water above the seat of explosion, or the shock felt from the 
ground closely adjacent to it, as marking that instant seems to 
me, in either choice, to neglect many sources of error. 
ing unable to read my paper personally, he has not fully 
understood the manner in which the instant of the starting of 
the wave was fixed. The great mine was fired by a mecban- 
ical drop, which closed simultaneously all the twenty-three elec- 
trical circuits. One extra pin and mercury cup in this drop was 
provided by General Newton for my use, and the signal was 
absolute instant of closing the a A circuits was elevtrically 
i t is impossible that this 
records among themselves invalidate their accuracy. I have 
just shown how these apparent discrepancies are explained by 
