Page:Popular Science Monthly Volume 56.djvu/465

Rh which is often fifteen hundred feet or more in depth. A perforated weight is then strung on the wire, and when the torpedo is in place the weight is allowed to fall, strike the cap, and explode the charge.

Dynamite has been used to knock out the blocking from the ways when launching ships. Fired on an iron plate placed on the top of a pile and covered with a tamping of earth or clay, it has successfully and economically replaced the pile driver. It has been found efficient in excavating holes in which to plant telegraph and telephone poles; in driving water out of quicksands in which foundations are to be laid or shafts to be driven; in slaughtering cattle; in breaking down ice dams to prevent inundations; in blowing up buildings to prevent the spread of conflagrations; in razing unsafe walls of burned buildings; in destroying wrecks which endanger navigation, and even in freeing vessels which arc hard aground on shoals.

An especially notable instance was in the blasting out of the débris in the river at Johnstown after the frightful flood that occurred there, which formed an enormous dam above the bridge and threatened its existence, and which was successfully and expeditiously removed by blasting after all other means had been tried in vain.

In fact, the amount of explosives consumed in the industries is so great that the quantity employed for military purposes sinks into insignificance. Yet we have failed to refer to those industries—quarrying and mining, and the engineering operations—in which they are most extensively and commonly used, being employed so largely in mining alone that it is an almost daily occurrence for blasts containing twenty, thirty, and even fifty thousand pounds of explosives to be used in a single charge; and