116 ANNUAL OF SCIENTIFIC DISCOVERY. 



to the air for a day or two the spirit evaporated completely, and at 

 the same time gave the deliquescent salt in the powder an opportu- 

 nity of absorbing the necessary amount of moisture. The large mag- 

 net apparatus and a supply of suitable fuses composed a portion of an 

 equipment fitted out during the late Chinese war for the purpose of 

 clearing away the obstructions in the Peiho river.. 



Since that period an extended series of experiments has led to 

 important improvements in the magnet-fuse. The priming composi- 

 tion is made more sensitive by the employment of a mixture of phos- 

 phide and sulphide of copper and chlorate of potash, instead of the 

 moistened gunpowder, and is now so readily ignited that single fuses 

 may be fired by the smallest magneto-electric machines, such as the 

 American apparatus (a six-inch horse-shoe magnet and rotating ar- 

 mature), recently introduced for medical purposes. 



Professor Wheatstone, who has been associated with Mr. Abel 

 throughout the course of these experiments, has contrived a very 

 ingenious and portable form of magneto-electric instrument, called 

 by him the "magnet exploder." This will fire a number of fuses, 

 either simultaneously or in succession, according to the arrangement 



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of wires employed, on merely turning the handle of the instrument 

 and pressing the stud or key, when the requisite velocity of the revo- 

 lution of the magnet-armatures has been attained, and the precon- 

 certed signal given. For the purpose of establishing metallic commu- 

 nication between the magnet-fuses and the " exploder," one insulated 

 wire is all-sufficient ; this need be but of small size, and, being led 

 out from the machine, is inserted into one eye of the fuse-head ; the 

 other requires merely to be connected with the ground by a short 

 length of ordinary copper wire attached to a small metallic plate 

 buried in the earth close at hand. All that remains to be done in 

 order to complete the earth-circuit is to connect the second binding 

 screw of the " exploder " with the ground beneath, using a similar 

 plate, or, more conveniently, a short wire passed under and dug in 

 with a spade. In the event of a number of charges requiring to be 

 fired simultaneously (frequently the case in engineering operations), 

 the distant extremity of the main wire is placed in communication 

 with a corresponding number of short branches of insulated wire, each 

 leading to a mine ; the juncture of the main wire with the branches 

 is effected by twisting the bare ends together with pliers, binding the 

 joint round with fine copper wire to insure proper connection through- 

 out, and then simply covering it with sheet caoutchouc or water-proof 

 canvas, to maintain perfect insulation. The ground wires of the series 

 of mines are, for greater certainty, collected into one, and secured as 

 a single earth connection. With ordinary attention bestowed upon 

 the repair of any injuries which the insulated wire may accidentally 

 sustain in the course of rough usage, no difficulty is experienced in 

 directing the operations at a great distance from the scene of the ex- 

 plosion. The use of ordinary uncovered wire, supported above the 

 ground on poles or stakes, provided with insulators, was referred to 

 as another means of conveying the magnetic current to a distance. 



The modifications rendered necessary in the general arrangements 

 for the carrying out of submarine explosions were briefly described. 

 The obstacles in the way of success were represented to be greater 



