ELECTRICITY FOB BLASTING 201 



central perforation still remaining free to receive the top of the quill or copper-tube, 

 which is charged with gunpowder in the same manner as the ordinary tube arrange- 

 ment for firing cannon. 



The plan originally suggested by M. Savare, of arranging the charges in divided 

 circuits was next tried, and furnished far more successful results. The simultaneous 

 ignition of twenty-five charges was repeatedly effected ; and forty charges were simi- 

 larly exploded on several occasions. These results were all obtained with the large 

 magnet constructed by Henley, the current being established by rapidly separating 

 the armature from the poles by means of a lever. By a simple arrangement for 

 shifting the connection of the main wire with the exploded charges from them to a 

 second series, similarly arranged, twenty-five were almost simultaneously ignited on 

 allowing the armature to return to the poles of the magnet. 



' The system of firing charges by means of magneto-electricity, with the aid of the 

 phosphide-of-copper fuze, having been thus far successfully developed, a series of 

 experiments was instituted at Chatham, for the purpose of thoroughly testing its 

 certainty and applicability in the field, and subsequently for ascertaining the extent to 

 which it admitted of application to the explosion of submarine charges. These expe- 

 riments extended over a period of six months, and were performed under various 

 conditions of weather. It will readily be understood that the best and most simple 

 method of connecting the fuzes, enclosed in the charges, with the branch-wires and the 

 earth, of arranging file experimental charges for explosion, and of carrying out the 

 various small but essential details involved in the operations, were only gradually 

 arrived at; and that, consequently, in many of the first experiments, which were 

 only partially successful, the failures were traced to causes unconnected with the 

 efficiency of the magneto-electric apparatus, or the fuze. It would be superfluous to 

 enter into details with regard to those preliminary experiments, however important 

 they were at the period of the investigation; the description of the operations at 

 Chatham will therefore be confined to those which were carried on according to 

 the plan winch was ultimately proved to be most efficient. The magneto-electric 

 apparatus employed in all the field experiments was Mr. Wheatstone's arrangement 

 of six small magnets, the whole apparatus having been enclosed in a box, so that the 

 only exposed portions were the binding screws for the attachment of the wires, a 

 handle for setting the armatures in motion, and a key, by the depression of which, 

 at a given signal, the circuit could be completed. 



To employ the instrument at any moment, only the following operations were 

 necessary : tie insulated wire and the copper wire passing to the earth were fixed to 

 the apparatus by means of binding screws: the instrument was raised from the 

 ground by being placed on its packing-case ; at that height, a man could operate 

 with it when in a kneeling posture. At the signal ' Ready ' the handle was turned 

 with ^ one hand, so as to cause the armatures to revolve with the greatest possible 

 velocity, whilst the other hand was pressed against one corner of the instrument 

 close to the key, so as to steady the box and to be ready, at the signal ' Fire,' to 

 depress the key with the thumb. 



The connection of the instrument with the earth was effected as follows : a mode- 

 rately clean spade was selected from among those used by the men in digging holes 

 for the charges. One end of a piece of stout copper-wire was placed under the edge 

 of the spade, so that, when the latter was firmly forced into the ground, the wire was 

 pressed by the earth on both sides against the iron surface. The protruding wire 

 was wound once or twice round the bottom of the spade handle, and then attached 

 to the binding screw of the magnet. 



The gutta-percha covered wire used in the experiments having been in occasional 

 service at Chatham for some years, the coating had sustained some injury in two or 

 three places. Such defects were protected from possible. contact with the earth by 

 means of waterproof cloth or sheet India-rubber. The total length of wire used 

 was 881 yards, of which 600 were extended, lying along the ground. 



To the extremity of the covered wire a number (from 12 to 25) of pieces of similar 

 insulated wire, varying in length between three and six yards, and serving to connect 

 it with the individual charges, were attached in the following manner : about six 

 inches of the extremity of the main wire and of each of the branch wires were laid 

 bare and cleansed ; the end of the former was then surrounded with those of the 

 latter (placed in an opposite direction) and the whole tightly twisted together by 

 means of pliers, so as to be brought thoroughly in contact with each other and with 

 the main wire. The twisted wires were then bound round with moderately fine 

 copper-wire, which was made to bring every portion of the exterior of the bundle into 

 connection. The joint was made rigid with pieces of stick tied against it, and the 

 whole securely enveloped in a piece of waterproof cloth or canvas, to protect it from 

 damp and contact with the earth. 



