experience. The path of the torpedo is indicated by the dotted line p1 p2. It is even possible to diminish the disturbance still further by arranging the torpedo somewhat behind the position above assumed, so that on discharge the centre of gravity moves forward. This would in some degree compensate for the loss of weight as giving a less net change in the natural velocity. In the opinion of the author, however, it is not to be recommended, since it would result in the machine being catastrophically unstable (prior to the discharge of the torpedo), or would at least tend in that direction.
§ 74. Aeroplane and Submarine. It is well known that the submarine, although when submerged invisible to an observer or "look-out" on the deck of a warship or other vessel, is clearly visible, and may be readily located by an aeronaut from a sufficient altitude. The conditions are similar to those frequently noticed when fish in a river are seen clearly from a bridge, but are invisible from the river-bank. The torpedo-boat or destroyer when operating against the submarine is at a considerable disadvantage, inasmuch as when the latter is submerged the only visible sign of its presence is its periscope—a pole of a few inches in diameter, projecting some few feet out of the water. Ordinarily it is the point where the periscope "rips" the surface that forms the most conspicuous visible indication. Thus we may anticipate that, in the future, operations directed against the submarines of an enemy will involve the employment of aircraft, at least as a means of reconnaissance. It is an important fact that in this particular service the enemy (the submarine) has no power of offence; hence it is possible that the dirigible may prove itself as well suited to the work as the aeroplane. It is true that the modern submarine is being fitted with guns of light calibre, but these are only available after the vessel has come to
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