180 H. L, Abbot—Transmission of Earth Waves. 
there a difference in the rate of transmission of the shocks, due 
to differences in the intensity of the initial explosion 
The method adopted was to station two observers near each 
other at a carefully selected inland position; each observing a 
mercury seismometer, and holding in his hand the key of an 
accurate Morse register to record the instant of arrival and the 
duration of the tremor. These seismometers were the same 
instruments used at the Hallet’s Point explosion. They dif- 
fered from each other only in the optical power of the telescope, 
that designated A in the table having a magnifying power of 6, 
and that marked B of 12. 
A fuse in the electrical circuit which fired the torpedo, was 
bedded in the cartridge of a field gun directed toward the ob- 
sion of the shock, the rejection of all the observations made 
with type A follows as a matter of course. They are valuable 
as exhibiting the rate of advance of waves having a certain in- 
Lieut. Leach, using a power of 12, recorded of the second 
observation of September 12th (No. 12), “ The gunpowder wave 
was peculiar, in having a much more gradual increase than has 
been observed in dynamite shocks. I should say it was at 
least two seconds in attaining a maximum, whereas the dynam- 
