382 John LeConte—Sound-Shadows in Water. 
viewed from the experimenter’s situation on the top of the pile, 
fiz. 1, A’ and B’, indicate the two positions of the bottle in the 
preceding experiments. 
e experiments were varied by plunging bottles into the 
water in various positions around the pile, within and outside 
of its geometrical projection from the explosive center; and in 
all cases they were protected from injury when within the geo- 
metrical;shadow, and were shivered when outside of the same. 
e same results took place whether the bottles were filled with 
water or with air. 
The breaking of a glass vessel, by a sudden shock communi- 
cated by means of water, is a fact long known, and is illustrated 
by the old familiar class experiment of exploding a “ Prince 
Rupert drop” while its bulb is plunged into an ordinary apoth- 
ecary’s phial filled with water. 
13. riments with stout glass tubes.—The cylindrical glass 
tubes employed were about 6 feet long, and 1°5 inches in diam- 
eter, the glass being about 0°5 of an inch in thickness. They 
were covered by pasting cartridge paper over them, so as to 
dled the loss of fragments when breakage occurred. (See 
g. 2, M). 
The tubes were adjusted to a frame-work of wood so arranged 
(fig. 2, N) that they could be plunged ina horizontal position 
beneath the surface of the water behind the pile, the axis of 
the tube being at right angles to the plane of its shadow, 
and held there (the observer standing as before on the top), with 
the middle of the tube in the geometrical shadow, while the 
two extremities projected on either side about 2°5 feet beyond 
boundaries of said shadow. (Fig. 3, C and C’). In every 
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