17,8 
POPULAR SCIENCE REYIEW. 
As torpedoes are generally arranged in lines, it has been 
proposed to moor them at intervals along a heavy chain sunk 
to the bottom, two parallel chains being used where there is a 
current. Another suggestion is a modification of this, and pro- 
poses to use a sunken hawser, with branches and anchors at their 
ends. The advantages of this latter plan are the ease with which 
the anchors would be fixed in line, and the facility it affords 
for raising any anchor by lifting the slack of the main hawser, 
working along it till the branch hawser belonging to the re- 
quired anchor is reached, and then raising the branch in the 
same way. It is, however, not very likely that any plan of this 
kind will be adopted, as both possess great disadvantages, 
amongst them the danger of the chain or hawser which forms 
the main line of the system being grappled by an enterprising 
enemy. 
Before we leave this part of the subject we must say a word 
about moorings in a tideway. When the rise of the tide is 
inconsiderable, there is no need of taking it into account in 
arranging a torpedo defence; but where it rises 15 or 20 feet, if 
the torpedoes are moored with reference to the low-water line, 
they will be almost harmless at high water ; and if with refer- 
ence to the high-water line, they will be visible on the surface 
at low water. A medium must therefore be adopted, and the 
charges being increased so as to act through a greater depth of 
water, they must be moored a little below the surface at low 
water, and then they will still be within range at high water. 
Sometimes it will be impossible to prevent the torpedoes being 
seen on the surface when the tide ebbs ; in those cases the Con- 
federates used dummies, such as empty cases and barrels, to 
deceive the enemy. 
There are two ways of firing the charges of torpedoes — 
electrically and mechanically. As we have said before, the 
mechanical torpedo is the older form of the apparatus ; but as 
the electrical method of ignition is used almost without excep- 
tion now-a-days, we shall describe it first. Four things are 
necessary in a system of electrical firing — the battery which 
originates the current ; the insulated cable by which it is trans- 
mitted to the torpedo ; the fuze, which is fired by the current 
and ignites the charge ; and, finally, the firing-key, which com- 
pletes the circuit by connecting the battery and the cable. Of 
the first little need be said ; all that is necessary is a voltaic 
battery of moderate power.* In the Chatham experiments the 
* Other forms of apparatus are occasionally used. Frictional electricity 
cannot he employed with safety, as the passage of the electric fluid through 
one cable induces similar action in all the others in its neighbourhood, and 
thus seyeral charges may be fired instead of one. The Austrians used a 
