674 SCIENTIFIC PROBLEMS OF THE FUTURE. 



production of energy, and in a few minutes we should see it floating on 

 the water an inert and lifeless mass, instead of sporting about as lively 

 as ever, as we actually do see it. Now, wlience comes this enormous 

 difference in the power required to propel the porpoise and the torpedo 

 at the same speed? The answer to this question contains, as I sub- 

 mit, the true and proper line of develoi)ment of the marine engineering 

 of the future. 



No doubt we shall be told at once that steamships can not imitate 

 the movements of the porpoise, that his motion is a question of fluid 

 displacement and '' stream-line" action or effect, due to the sinuous 

 inflections of his body, and of his tail especially. This is i^artly +rue, 

 and it is not here contended that we can make ships with flexible back- 

 bones like a fish, and give them a fish-like motion. Nevertheless it 

 appears i^robable, if not certain, that the main and essential cause of 

 the enormous waste of power at present attaching to man's work, the 

 ship or the torpedo, when compared with nature's work, the porpoise 

 or the shark, is surface or skin friction. 



That skin friction is the leading agent in rendering necessary the 

 immense power required to pro2)el ocean steamers or battle ships through 

 the water is clearly recognized by the chief authorities on the subject, 

 such as Mr. White in his standard work on naval architecture. Herein 

 he only follows on the principles which were first, I think, formulated 

 by the elder Mr. Fronde, late investigator of marine problems to the 

 British Admiralty, in a paper read many years ago at a meeting of 

 the British association at Bristol. In order to clear away a prevail 

 ing misconception, or popular error, which quite vitiates any sound 

 argument on this whole subject, it seems necessary to refer to Mr. 

 Fronde's paper. Therein he demonstrated that the idea that the resist 

 ance to motion of a body through water is to be measured by " head'' 

 resistance, or the resistance of its cross secti<m, to passage through the 

 water is baseless and mistaken. There is really no such thing as head 

 resistance, so that if a fairly well-designed body, such as a torpedo, were 

 entirely immersed in a perfect fluid and started in motion at any given 

 speed it would, if there were no surface friction, continue to move 

 uniformly in a straight line ad infinitum. The result of this law, as 

 applied to water, which is not quite a perfect fluid, but has some small 

 amount of viscosity, is that very nearly but not quite all — about 98 per 

 cent, speaking approximately from memory — of the total resistance to 

 the motion of such a torpedo underwater is due to skin or fluid friction. 

 Any consideral)le reduction therefore in this friction avouUI efl'ect a very 

 large corresponding gain in the speed of the submerged body, or a 

 diminution in the power required to propel it at the same speed. 



When we come to deal with the case of bodies only partly submerged, 

 such as shii3s, the matter is not .so simple, as a very appreciable fraction 

 of the total resistance to motion is due to the action of waves and wind, 

 and involves a consideration of length, depth, etc., on the part of the 



