172 
POPULAR SCIENCE REVIEW. 
nothing. The German harbours, with tliis new defence, were 
almost impregnable, and they were not attacked. So well 
satisfied is the German government with the experience of 1870, 
that it is said that they have decided to build no more men-of- 
war for the present, but to devote the funds which would 
otherwise be used for this purpose to the construction of floating 
batteries and the acquisition of torpedo materiel for the defence 
of their coasts and harbours. 
With this brief sketch of the history of torpedo warfare we 
must pass on to an account of how it is conducted. We shall 
speak first of fixed torpedoes, and the way in which they are 
secured in position and fired so as to do their work ; then we 
shall go into the general principles of harbour and coast defence ; 
and finally we shall briefly refer to the most successful efforts 
which have been made to construct effective locomotive torpe- 
does — a branch of the subject which is not yet so far advanced. 
The first thing necessary in the construction of a torpedo is a 
case in which to place the charge. This case must be perfectly 
water-tight, otherwise the explosive will be rendered useless by 
the water leaking into it; and to secure this it must be strong 
enough to bear a good deal of rough handling, and also the 
pressure of the water at the depth to which it is to be submerged. 
When (as is usually the case) it is to be floated up from an 
anchor, it must have, when loaded, sufiicient buoyancy to keep 
it steady at its moorings. It must be of such a shape that the 
charge may be readily and completely ignited with as few fuzes 
as possible ; and as with gunpowder, or gun-cotton with an 
ordinary fuze, the explosion is not instantaneous in a charge of 
any size, but as it were runs through it, the case must be strong 
enough to hold together for a moment till the whole explosive 
force is developed; otherwise the first portion of the charge 
ignited will burst it, and admit the water to the rest. Various 
forms of case and various materials have been used or suggested. 
For their smaller torpedoes the Americans employed wooden 
barrels, and for the larger kind cases made of boiler-plate, and 
not unfrequently they used steam-boilers for this purpose. The 
barrels would of course be strengthened at the heads, and every 
kind of extemporised case would have to be made thoroughly 
water-tight by being coated either inside or outside with tar or 
some other waterproof material. The torpedoes for the defence 
of the Venetian coast in 1866 had either iron or wooden cases. 
(See figs. 1 & 2, PI. XCVIII.) The former consisted of two 
cylinders, one within the other ; the inner one contained the 
charge, and the space between them was left empty, to give 
buoyancy to the whole. The outer case was about 4 ft. high and 
4 ft. in diameter, and the charge was 3 cwt. of gun-cotton. The 
wooden cases were also double, the space between them being 
