662 



HISTORY OF THE SEA. 



keep them from getting filled with dirt. As soon as the charges 

 are placed, the diver returns to the boat, and it drops far 

 enough from the spot, to be safe from the effects of the ex- 

 plosion, and then, with a few turns of the battery, the nitro 

 glycerine explodes. Two muffled explosions are heard, the 

 one transmitted 

 through the water 

 and the other 

 through the air, 

 and on the instant 

 a volume of water 

 is hurled perhaps 

 fifty feet into the 

 air, while through 



the mass jets of water are hurled in all 

 directions two or three times further, 

 together with fragments of rock. The 

 water subsides quickly, and round the 

 spot dead fish come floating to the top, 

 killed by the shock of the explosion. 

 At each blast the rock is broken up 

 over an area of four or five hundred 

 square feet, and the fragments are re- 

 moved by a grappling machine. putting in the charges. 



In these submarine operations the divers use the armor 

 which the discovery of india rubber and the process of vul- 

 canizing it has made possible, enabling the diver to descend, 

 and leaving him liberty of movement enough to work. In 

 this, as in almost every other new method, there have been 

 gradual steps of improvement and development. During the 

 latter part of the last century the plan was proposed for the 

 diver to carry down with him a supply of air, compressed into 

 a reservoir which he wore on his back, inhaling the air through 

 a tube. Mocked arrangements of this method were in use 



