The water spout produced by the explosion sometimes completely covers the torpedo boat, and the latter would be sunk by it were not all apertures closed so as to make her a true buoy. What appears extraordinary is that the explosion does not prove as dangerous to the assailant as to the adversary. To understand this it must be remembered that, although the material with which the cartridges are filled is of an extreme _shattering_ nature, and makes a breach in the most resistant armor plate, when in _contact_ with it, yet, at a distance of a few meters, no other effect is felt from it than the disturbance caused by the water. This is why a space of 12 meters, represented by the length of the torpedo spar, is sufficient to protect the torpedo boat. The attack of an ironclad, however, under the conditions that we have just described, is, nevertheless, a perilous operation, and one that requires men of coolness, courage, and great experience. [Illustration: ATTACK BY A TORPEDO BOAT UPON AN IRON CLAD SHIP OF WAR.] There is another system which is likewise in use in the French navy, and that is the Whitehead torpedo. This consists of a metallic cylinder, tapering at each end, and containing not only a charge of gun cotton, but a compressed air engine which actuates two helices. It is, in fact, a small submarine vessel, which moves of itself in the direction toward which it has been launched, and at a depth that has been regulated beforehand by a special apparatus which is a secret with the inventor. The torpedo is placed in a tube situated in the fore part of the torpedo boat, and whence it is driven out by means of compressed air. Once fired, it makes its way under the surface to the spot where the shock of its point is to bring about an explosion, and the torpedo boat is thus enabled to operate at a distance and avoid the dangers of an immediate contact with the enemy. Unfortunately this advantage is offset by grave drawbacks; for, in the first place, each of the Whitehead torpedoes costs about ten thousand francs, without counting the expense of obtaining the right to use the patent, and, in the second place, its action is very uncertain, since currents very readily change its direction. However this may be, the inventor has realized a considerable sum by the sale of his secret to the different maritime powers, most of whom have adopted his system.