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POPULAR SCIENCE REVIEW. 
four crusher gauges, each crusher piston § square inch in area ; 
behind it was a lead pellet hardened with antimony. Over 
each side of the vessel were suspended six 18-pounder shot, also 
fitted with crusher gauges. The object of these preparations 
was to put the vessel into the condition representing that in 
which an enemy’s ship might receive the attack. It had been 
urged that a specially vulnerable point was to be found in the 
condensers and their fittings. Hence the attention given to 
them. With respect to the weight of the vessel, it will be 
readily seen that in the kind of attack that was to be made the 
inertia of the vessel affected the question directly. If a small 
charge, and such as might be driven against the side of a vessel 
by a locomotive torpedo, were exploded in contact with the 
ship’s side, the effect would be localised, and the weight of the 
vessel under these conditions would not enter into the question ; 
for the blow delivered is of such a character that the vessel 
cannot escape injury in any degree by being lifted or moved. 
The whole effect, whatever it be, must be expended on the 
part of the ship presented to it. It is otherwise with a large 
ground mine. The charge being exploded perhaps 50 feet from 
the ship’s side, in place of a small force acting on a surface of a 
few superficial inches, the ship receives the effect of a much 
greater blow, but already distributed not exactly over the sur- 
face of a sphere of 50 feet radius, but in a somewhat similar 
manner. Water being incompressible, deli&ers the blow of the 
explosion well ; being, in fact, compelled to move to make room 
for the gas suddenly generated. W ith an incompressible medium 
round it laterally and earth beneath, it is evident that the only 
direction in which movement is possible is upward ; and the 
water being lifted more directly and easily, just in proportion 
as it is situated more nearly above the charge, the chief dis- 
placement is directly upwards, a mass of water being driven into 
the air, as shown in Plate CXXVIL, which is a sketch made 
from the actual jet of water thrown up on the occasion of the 
first Oberon experiment, but which equally well represents that 
of almost any submarine explosion. 
From this it follows that the blow falling on a ship consists 
in a sudden forcing of the water against a large part of the side 
or bottom, and it is evident that the damage done to her may 
be less in the case of a light ship that moves readily than a 
heavy one. A ship heavily weighted with armour, then, would 
expose her bottom to a more severe shock than any other class 
of vessel. The Oberon , consequently, did not perfectly repre- 
sent an armour-clad vessel, although her bottom corresponded to 
that of the Hercules , but she probably was sufficiently like to 
answer the purpose in view. The object of the crusher gauges 
was to register the pressure of the water in all directions, with 
