104 HARBOUR CONSTRUCTION. 



is inserted, just as the end of a piece of ordinary slow fuse would 

 be, the wires from it being coupled up with those from the 

 battery. The charge may then be fired at pleasure. The battery 

 wires ought on no account to be connected with the battery 

 until all is ready for firing. 



Fuses, A good substitute for electricity in firing several 

 charges simultaneously has been invented by Messrs. Bickford, 

 Smith & Co., the well-known fuse manufacturers. 



It consists of several lengths corresponding with the number 

 of " shots " to be fired of what is termed " instantaneous " or 

 " lightning " fuse, the ends of which are brought together into a 

 small cylinder called an " igniter." This contains an explosive 

 disc, against which the ends of the several lengths of instan- 

 taneous fuse rest, and which ignites them all simultaneously 

 when fired by means of a single ordinary safety-fuse, which 

 enters the " igniter " at the opposite end. The other ends of the 

 instantaneous fuses are placed in connection with the several 

 charges in precisely the same way that ordinary fuses would be. 



The instantaneous fuse burns at the rate of 150 feet per 

 second; consequently, if the lengths leading to the several 

 charges measure approximately the same, the charges will all be 

 fired at the same instant. 



When electricity is not used, single charges are generally 

 fired by means of the ordinary "Bickford" safety-fuse. This 

 fuse is supplied in several qualities to meet the various con- 

 ditions under which it may be employed. The rate at which 

 it burns varies slightly, but is generally from 2 to 3 feet per 

 minute. 



