John LeConte—Sound-Shadows in Water. 37 
portional to the time ponapier by the displacing impulse, mal- 
tiplied by the velocity of transmission of the elastic pulse. 
In algebraic terms, if L=wave-length, ‘=time of the genera- 
ting impulse, ones v=velocity of sound in tae elastic medium ; 
we “have, L varies as tXv; or L=txv. Consequently, in a 
given medium, in w tok v remains constant, L will be a fune- 
tion of ¢, or the duration of the generative Aa oid so that 
when the factor ¢ is indefinitely small, the value of L will be 
correspondingly small. Hence, when the he o the blow or 
explosive impulse is exceedingly brief, the wave-length must 
be hel parse shor 
. Application to ae Shadows.—In the experiments of 
Colluden, if we assume that the brief shock of the hammer on 
a limited portion of the bell was alone transmitted to the dis- 
tant observer, it is asa that only the short sound-waves thus 
generated would + neh: the distant obstructing wall or screen 
in the water: and consequently the greater definiteness of the 
acoustical shadows in water as compared with those in air 
would ie necessary result of the greater shortness of the 
sound-waves in water. Under the foregoing assumptions, the 
theory of aodulation: appears to afford a satisfactory explana- 
tion of the phenomenon observed by Colladon. Nevertheless, 
it would have been extremely interesting and instructive, as 
a very severe test of theory, had this distinguished physicist 
made observations on the relative distinctness of the sound- 
shadows in the water within the musical range of the sub- 
merged bell, as compared with those observed at points so re- 
mote that only | the sharp blow of the hammer was audible in 
the water. 
In like manner, the application of the digas ie of briefness 
of elastic-wave- genesis to the explanation of the phenomena 
observed by my son in his “‘ Dynamite” experiments, is suffi- 
ciently obvious. In fact, all the phenomena incident to the 
explosion or detonation of the nitro- glycerine compounds indi- 
cate that the impulse generated is of indefinitely brief dura- 
tion; indeed, its suddenness is almost beyond guano 
Thus, a dynamite cartridge placed upon a log of woo 
fined and free, with nothing above it exce ot the abboisen. 
will, when exploding, shiver the portion of timber under it to 
the heavy ara - gents Point, Hell Gate, in the harbor of New York, 
Seem to rende t probable, that the wayes transmitted by the earth, 
reached the aifistant observers in groups, or as a train of waves. (This Journ., 
ses Xv, a D. 178 et 
_Sir G.B B. + inabilnadin that “there is reason to think that a —_— wave in 
air or in the ‘eapihues of light would not produce the sensation of soun color.” 
(Undulatory Theory of Optics, p. 15, Art. 18,—1866). No reason pi oe ad 
for this somewhat extraordinary assertion. In the case of light it is obviously 
ccna to experimentally test the Mpeg of this idea of the former Astron- 
r Royal; and it does not appear to be sustained by the results of acous- 
eal experiments. 
