First, let us consider the general effect of a submarine explosion. It closely resembles the action of gunpowder when ignited in a gun. We know that in the latter case a quantity of heated gas is formed, which in its power of expansion exerts force in all directions. Prevented from expanding by its rigid confinement, except in the direction of the bore, the gas attains its object by the displacement of the projectile. This is, in fact, the line of least resistance. When the same explosive is ignited under water, the heated gas presses outward in all directions, forcing the surrounding molecules of water against their neighbors, which are, in turn, propelled forward with great violence. This effect continues until the back pressure of the liquid medium equals the now reduced pressure of the gas due to its expansion in the space vacated by the displaced water, which is likewise to some extent compressed by the action of the gas. Though brought actually to a state of rest, the surrounding water is under the influence of great pressure, which by the law of fluids is transmitted equally in all directions. When a vessel is sufficiently near the explosion to be struck by the water which has been so violently disturbed, it will act upon her like a huge projectile, and it is obvious this range will be in proportion to the amount of explosive employed. This, combined with the resistance her hull offers, will also determine the effect produced. If the charge is too near the surface of the water, the liquid layer above it will not restrain the liberated gas sufficiently to allow of its full power being exerted in other directions, and hence permits its escape into the atmosphere, throwing up the water in its way to a greater or less height, according to the thickness of the layer. The spectacular effect, therefore, afforded by the upheaval of a large and lofty column of water is no criterion of the efficiency of a submarine explosion, but, on the contrary, shows that much of its energy has been expended in the wrong direction. The amount of submersion to give the greatest lateral effect to different charges of explosive has been ascertained by practical experiments. For 100 lb. of gunpowder, it is stated to be 10 ft., while for the same quantity of guncotton it should be 15 ft. As the charge employed against the Resistance was 90 lb. of guncotton placed 10 ft. below the surface, it is probable that some loss of power was sustained in the manner we have indicated. At a greater depth also the charge would have been to some extent under the vessel, where its explosive effect would have been more severe, and where the construction of the hull cannot be as strongly fortified with coal as was the case in the Resistance. We are unable to state why a depth of 10 ft. was selected on this occasion; but it may be due to the fact that up to a late date most of our locomotive torpedoes have not carried a larger charge than 40 lb. of guncotton, and are usually run