38 John Le Conte—Sound-Shadows in Water. 
atoms :—The detonation being so instantaneous, that the su- 
perincumbent air, as well as the gases gen nerated, having no 
The efficiency of surface oe under wean, by means of 
these explosive compounds, depends upon this extraordinary 
suddenness of detonation, hich renders the effect akin to that 
of the sudden blow of an enormous unyielding mass. It is ev- 
ident, that the wave generated in an elastic medium like water, 
“a an explosion of this character, must be 7 intense wri 
piles on the glass vessels plunged in the water was narrowly 
circumscribed within the limits of the geometrical shadow, may 
be Sach traced to the extreme shortness of the elastic 
generative detonations. is view seems to afford a satisfac- 
tory explanation of the remarkable results revealed by the-ex- 
periments in the harbor of San Francisco 
18. Gun-powder explosions.—If the foregoing is the true ex- 
planation of the definiteness of the sound-shadows cast in the 
preceding experiments, then the waves generated by the ex- 
plosion of ordinary gun-powder, being less sudden, should not 
produce as sharply.defined shadows as those due to ‘the detona- 
tion of dynamite. We have, so far as known, no specific ex- 
pee testing this point, but it seems to be quite reasona- 
ble that such will be found to be the case, whenever the test 
of aaparmicnt is applied. For it is well cn n that ee se 
queous explosions of ordinary powder do t give rise to the 
remarkable concussions, so sel pha of as ees of 
the nitro- = yore mixtures 
sounds propagated through the air should vary with the sud: 
denness of the action of the generating cause. 
Inasmuch as the variations in the duration of the genesis of 
audible sounds in the atmosphere must, in ordinary experience, 
be very great, it may, at first sight, appear incredible that the 
eraeienniag differences in the perfection of sound-shadows 
t by obstacles in the paths of different kinds of sounds, 
steak have poten ee the most casual observation. But it 
4 bc les 
ae Ey ee re ee eR FRY a 
