TORPEDOES. 
179 
usual agent was a Grove’s battery ; a trough battery may also be 
used, but the best for the purpose are constant batteries, such 
as Bunsen’s or Daniel’s. One end of the battery, whatever it 
may be, is connected with the ground by an earth-plate ; the 
other is connected with the insulated cable by means of the 
firing-key, which for the present we shall leave out of con- 
sideration. There are several different patterns of cable. One 
of the strongest and best insulated is that which is made by 
the Hooper’s Cable Company. It consists of a copper con- 
ducting wire, A (fig. 9), surrounded by an india-rubber in- 
sulator, B, formed of three coats. The inner one is of raw 
india-rubber, and then comes one of india-rubber mixed with 
oxide of zinc. These two are very thin, and their object is to 
prevent the sulphur of the thick outer coat, which consists of 
vulcanised india-rubber, acting chemically on the copper of 
the conductor. When the cable is not likely to be subjected 
to any rough usage, it is completed by placing a covering of 
india-rubber felt over the insulator ; but as in most . cases 
something stronger would be required, the insulator is usually 
covered with tarred hemp, c, and where the bottom is rocky 
an additional protection of wires and tarred hemp, d, is added. 
This cable is laid from the firing point along the bottom, and 
enters the torpedo by a water-tight and insulated joint, and 
there the conducting wire is attached to the fuze. 
Of fuzes there are dozens of patterns, of which we shall 
describe two or three, to illustrate the principle on which they 
are constructed. Some require a powerful current of large 
quantity ; others, on the contrary, can be fired with a current 
of very high tension. Of the former the best example is the 
platinum-wire fuze, which acts by a strong current melting a 
small piece of platinum wire placed in the circuit and , sur- 
rounded by a priming charge which the heated wire ignites, 
and in this way the torpedo is fired. Fig. 5 shows the usual 
1 form of this fuze ; E is a small solid cylinder of ebonite with a 
shoulder at the top, which fits into a corresponding shoulder in 
* the torpedo case, a a, in the loading-hole of which the fuze is 
' inserted. Where the shoulders meet, a ring of vulcanised 
I india-rubber is placed to act as a packing between them, and 
I make the joint water-tight, and they are held firmly together by 
, the ring or hollow screw, bb, which fits a female screw cut in 
! the inside of the loading-hole. Two wires, CF, df, are passed 
I through holes in the ebonite cylinder, a watertight composi- 
tion being forced in round them ; they project a little below it, 
I being about of an inch apart, and are connected by a piece 
j dynamo-electric apparatus specially designed for tlie purpose, and electro- 
i magnetic coils have also been similarly employed. 
I 
