40 



THE POPULAR SCIENCE MONTHLY. 



ric shadow determined by lines supposed to be drawn from the 

 cartridge forty feet horizontally away. The bottle was perfectly 

 protected from the shock of the explosion. It was then put in 

 front of the pile. The first shock shivered it into hundreds of 

 fragments. Other bottles, some filled with air and some with 



SA/VO STONE REEF ' 



M 



Fig. 1. 



water, were similarly exposed in various directions around the 

 pile, and with the same result destruction, except when within 

 the protecting shadow. The experiments were varied by immers- 

 ing stout glass tubes (Fig. 1), incased in thick paper, horizontally 

 across the direction of the sound-rays in water, between two piles 

 which were aligned with the dynamite cartridge. These piles were 



twelve feet apart, the 

 nearer one being forty 

 feet from the cartridge. 

 Its shadow, therefore, 

 just covered the second 

 pile, and included the in- 

 termediate water, with 

 the middle part of each 

 tube. After an explosion 

 these protected parts 

 were found to be un- 

 broken, while the ends 

 which projected on the two sides beyond the shadow were com- 

 pletely shattered (Fig. 2). The boundary between the regions of 

 shadow and noise was sharply defined on the tubes, even at a dis- 

 tance of twelve feet behind the protecting pile. 



To account for the shortness of the sound-waves which were 



Fig. 2. 



