John Le Conte—Sound-Shadows in Water. 31 
ll. Effects of the explosive shock—It was observed that the 
suddenness of the shock imparted to the water by this explosive 
agent produced the most remarkable and astonishing effects. 
At the distance of 300 feet or more from the detonating car- 
tridge, two distinct shocks were experienced. The first shock 
came through the intervening water, and was felt as a short 
concussion or click before there was any sensible elevation of 
the column of water resting over the point of explosion. The 
second shock came a little later by the air, and was heard. It 
was evidently communicated to the air by the water, at the time 
the elastic pulse transmitted by this liquid (the first shock) 
emerged, in a direction nearly normal to its surface, over a lim- 
ited area around a point vertically above the exploding car- 
tridge. This was obvious from the fact that aerial sound came 
from this region. The area, which was the source of the sound 
transmitted by the air, was the same as that from which the 
small jets of water (noticed hereafter, 14) were projected. The 
gases generated during the explosion came to the surface much 
later than this shock, and after elevating the column of water, 
over the position of the cartridge, to the height of twenty-five 
or thirty feet. 
_ It is the character of the first shock that deserves special no- 
tice. Toa person sitting in a small boat floating on the water | 
at a distance of 800 feet or more from the point of explosion, 
with his feet resting on its bottom, the shock was felt as a sudden 
blow applied to the soles of the feet. In fact, it drove out the 
oakum from the seams in the bottom of the boat. When the 
observer stood on the top of a vertical wooden pile, this shock 
was felt as a sudden concussion coming up from the water along 
the cylinder of wood. The concussion produced by such an 
explosion was so violent that it killed or stunned the fish in 
the water within a radius of 200 or 300 feet from the explosive 
center. They rose to the surface in a helpless condition, and 
were secured by the boys. 
EXPERIMENTS ON Sound. SHADOWS. 
12. K periments with stout glass (soda-water) Bottles.—In 
these experiments the observer stood on the top of a vertical 
cylindrical pile (the trunk of an Oregon pine) about one foot in 
diameter, situated about forty feet horizontally from the explo- 
Sive cartridge. The bottle being secured to a rigid rod was 
rst plunged under the water from ten to twelve inches behind 
the pile (fig. 1, A), that is, within its geometrical shadow. The 
shock of the explosion did not injure the bottle. It was then 
plunged into the water in front of the pile (fig. 1, B), or out- 
side of its geometrical shadow. In this position the bottle was 
shivered to atoms by the concussion due to the explosion. As 
