34 John LeConte—Sound-Shadows in Water. 
of the pile casting the shadow. Hence, the shadow of the 
cylindrical pile extended back for about 12 feet between sensibly 
parallel vertical planes, and its boundaries, at this distance, were 
still sharply defined. 
It is evident that, if the explosive center were of insensible 
magnitude, the horizontal thickness of the geometrical shadow of 
the pile, at a distance of 12 feet beyond it, would be augmented 
in the ratio of 40 to 40+12, or of 40 to 52; these numbers 
being the distances in feet from the center. So that, if the 
thickness of the shadow at the pile were 12 inches, its thickness 
at 12 feet beyond would be 15°6 inches. If, however, the ex: 
plosive energy occupied more or less space (as was the case in 
relation to the ‘“ giant-powder” 
thickness of the shadow would diminish with increasing dis- 
tance from the obstructing pile; asin the case of the umbra 
cast by an opaque body which is smaller than the luminous 
source. 
14. Another phenomenon observed.—Another interesting pbe- 
nomenon came under notice during the execution of these ex- 
periments. It was the singular effects observed on the surface 
of the water (when perfectly calm and glassy), for a certain 
area around the point immediately over the exploding cartridge. 
Simultaneous with the first shock (11) transmitted by the water 
—and before the ascending gases of explosion disturbed it—the 
surface of the liquid exhibited numerous jets of water, rising 
to the height of about 8 inches over the center of the area, and 
diminishing in height with augmenting distance from the center. 
he appearance presented was not unlike that produced by a 
heavy shower of rain falling on the calm waters of a lake, 
(fig. 4). To an observer in a boat floating on the adjacent ~ 
i from 
water, and consequently viewing the phenomenon 
point near the water-level, there seemed to be a curious quin- 
cunx-like arrangement of the jets. 
see 
esas bors nity hs 
he Soe oy Dyce er Aga ee a a 
a 
4 
3 
= 
: 
: 
3 
