John LeConte—Sound-Shadows tn Water. 39 
must be recollected, that, for the reasons already assigned (1), 
(2), (8) and (4), aerial acoustical shadows are not readily appre- 
ciated by the ear. oreover, in the case of sounds transmit- 
ted by the air, the distinctness of such shadows is most seri- 
ously impaired by the numerous reflected waves which come 
from circumjacent objects. It should be borne in mind, that 
it 18 only very recently (5), that the influence of acuteness of 
sounds on the distinctness of the resulting shadows, has been 
satisfactorily verified by experiment. In like manner I ven- 
ture to predict that careful experiments will verify the deduc- 
tion that the shadows due to sounds generated by the extra- 
ordinarily brief detonations of dynamite are more sharply 
defined, than those owing their origin to sounds less suddenly 
produced. 
In confirmation of the foregoing view, the following obser- 
vation may be cited: On the 16th of April, 1880, an explosion 
of about 2000 or 3000 pounds of a nitro-glycerine compound 
occurred at the “Giant Powder Works,” situated under a bluff 
on the eastern shore of the Bay of San Francisco, at a distance 
(determined by triangulation), of 16,201 feet (4938 meters), in 
a direct line, in a northwest direction, from my room in the 
University building. About twenty-five adult men, a majority 
of them China 
structure completely cut off the sound-wave coming by the 
alr. it is searcely necessary to add, that for ordinary sounds 
such would not have been the result. 
0. Phenomenon of Jets.—The singular phenomenon ob- 
served by my son (14), of numerous small jets projected from 
the surface of the water when the shock transmitted by the 
liquid reached the surface-area above the exploding cartridge, 
Was probably due to the circumstance that when the short and 
tense elastic wave emerged in a direction normal or nearly 
hormal to the aqueous surface, the tense superficial capillary 
film yielded to the sudden impulse more readily at some points 
