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the explosion forms a crater in the mud ; but where it is hard 
and rocky, it is reflected upwards, and adds considerably (at 
least 30 per cent.) to the effect of the charge. One scale used 
by the Confederates began at 300 lbs. of gunpowder for two 
fathom water, and to this 300 lbs. were? to be added for every 
additional fathom. A scale proposed for gun-cotton begins at 
125 lbs. at depths not exceeeding 20 feet, and goes on to 500 lbs. 
for depths greater than 40 feet. This is, however, one of the 
many points connected with torpedo warfare on which we have 
still much to learn. 
We have now supposed the case for the torpedo and the 
explosive it is to contain selected ; the next thing to decide 
upon is, how it is to be secured in its place, and how it is to be 
fired. Where the depth of the water is inconsiderable, the 
torpedoes are usually weighted to deprive them of all buoyancy, 
and then sunk to the bottom ; but in the defence of the mouths 
of great rivers and large harbours it is generally necessary, on 
account of the depth of water, to moor them in position. 
It would seem, at first sight, a very simple matter to anchor a 
torpedo at a previously selected point ; but the fact is that the 
mooring of the torpedoes is the most difficult operation in the 
arrangement of a system of defence. The sea, or even the 
surface of a large harbour, is seldom perfectly smooth, and a 
slight breeze, the rise and fall of the tide, a current, or the 
flow of a river, all put obstacles in the way. Several points 
have to be attended to in fixing a torpedo in position. It must 
be steady in one place, and that place must be accurately 
known ; there must be on the surface no indication of the pre- 
sence of danger ; and, lastly, there must be as little twisting of 
the mooring lines by the current as possible, otherwise the 
insulated electrical cable of the torpedo might be injured. 
According to circumstances, from one to three moorings, con- 
nected with anchors or heavy weights, are attached to each 
torpedo. The Austrians in 1866 used a triangular wooden 
platform, heavily weighted, and having a mooring-line fastened 
at each angle. But this method of fixing the torpedoes was 
used in the Adriatic, an almost tideless sea, where there was no 
danger of the moorings twisting and entangling. The form of 
anchor used in English experiments was generally what is 
called a crab-anchor — a dome-shaped mass of metal, with points 
round the circumference of its base to take hold of the ground. 
The torpedo is attached to this by a mooring-line of wire-rope, 
of such a length that the charge is kept at the required depth 
below the surface. There are two methods of effecting this. 
The anchor and the torpedo may be fastened to the mooring- 
line at the proper distance apart, and then both together may 
be lowered into the sea. But it is found to be almost impos- 
