198 ELECTRICITY FOB BLASTING 



spark brings about an explosion. But it is necessary to take care when the fusee has 

 been prepared, as we have pointed out, to try it in order to regulate the extent of the 

 solution of continuity. It might, in fact, happen that while still belonging to the same 

 envelope of a copper-wire, the sheath of a vulcanised gutta-percha with which the 

 fusee is furnished, may be more or less impregnated with sulphide of copper ; 

 now, if the sulphide of copper is in too great quantity, it becomes too good a 

 conductor, and prevents the spark being produced ; if, on the contrary, it is not in a 

 sufficiently large quantity, it does not sufficiently facilitate the discharge. 



The first trials on a large scale of the application of the process that we have just 

 described were made with Kuhmkorff's induction apparatus, by the Spanish colonel, 

 Verdu, in the workshops of M. Herkman, manufacturer of gutta-percha covered wire, 

 at La Villette, near Paris. Experiments were made successively upon lengths of wire 

 of 400, 600, 1,000, 5,000, and up to 26,000 metres (of 3'28 feet each); and the success 

 was always complete, whether with a circuit composed of two wires, or replacing one 

 of the wires by the earth ; two ordinary Bunsen's pairs were sufficient for producing 

 the induction-spark with Kuhmkorff's apparatus. Since his first researches with 

 M. Euhmkorff, M. Verdu has applied himself to fresh researches in Spain ; and he 

 was satisfied, by many trials, that of all explosive substances, not any one was nearly 

 so sensitive as fulminate of mercury ; only, in order to avoid the danger that arises 

 from the facility of explosion of this compound, he takes the precaution of intro- 

 ducing the extremity of the fusees into a small gutta-percha tube, closed at the end. 

 After having filled with powder this species of little box, and having closed it 

 hermetically, the fuzes may be carried about, may be handled, may be allowed to 

 fall, and even squeezed rather hard, without danger. The elastic and leather-like 

 nature of gutta-percha, which has been carefully softened a little at the fire, preserves 

 the fulminate from all chance of accident. We may add, that with a simple Bunsen's 

 pair, and by means of Kuhmkorff's induction apparatus, M. Verdu has succeeded in 

 producing the simultaneous explosion of six small mines, interposed in the same 

 circuit at 320 yards from the apparatus. He has not been beyond this limit ; but ho 

 has sought for the means of acting indirectly upon a great number of mines, by 

 distributing them into groups of five, and by interposing each of these groups in a 

 special circuit. The fusees of each group are made to communicate by a single wire, 

 one of the extremities of which is buried in the ground, and whose other extremity 

 is near to the apparatus. On touching the induction apparatus successively with 

 each of the free ends that are held in the hand, which requires scarcely a second of 

 time, if there are four wires, that is to say, four groups and consequently twenty 

 mines, twenty explosions are obtained simultaneously at considerable distances. 

 There are no limits either to the distance at which the explosion may take place, or 

 to the number of mines that may be thus made to explode. 



The following account of experiments on the application of permanent magnets to 

 the explosion of charges and to submarine operations, is from a memoir by Professor 

 Abel, F.R.S. The ignition of gunpowder by the direct magneto-electric current, 

 though well known to be practicable, has never yet been applied to military or in- 

 dustrial operations, and no satisfactory experiments appear to have been made, before 

 those undertaken at Woolwich, showing its practical applicability to these purposes. 



In the first experiments on this application of the magneto-electric current, a very 

 large powerful magneto-electric machine was employed, which had been constructed 

 by Mr. Henley (and had been exhibited by him at the Paris Exhibition in 1855). 

 The principle of this instrument was precisely the same as that of the machine 

 devised by Mr. Wheatstone, for ringing magneto-electric bells. Its armature, instead 

 of being rotated, was suddenly detached from the magnet by means of a lever. It 

 was soon established by a few experiments that, even with this instrument, gun- 

 powder itself could not bo ignited with any degree of certainty. Results obtained 

 with Statham's and other fuzes, though superior to those furnished by gunpowder 

 alone, were still far from satisfactory. The first efforts wore therefore directed to the 

 discovery of a suitable agent to servo as a perfectly certain medium (or priming 

 material) for effecting the ignition of charges by means of the magneto-electric 

 machine. For this purpose, a variety of compounds and mixtures of a more or less 

 sensitive character were prepared for trial with the magnet. 



Many of these compositions furnished results to a certain extent favourable, a 

 number of fuzes, primed with them, having been fired in succession with the magnet, 

 and from two to four charges in one circuit having been ignited, in a very few in- 

 stances. But no perfect certainty of discharge was attained with any one of the 

 materials used ; the attempt to fire a fuze being frequently unsuccessful, while no 

 difference between it and a successful fuze, containing the same composition, could 

 be detected by careful examination. 



Some successful results, obtained accidentally with one of the experimental com- 



