Soiiw I^xperiinents in Propulsion. 9 



time, it may be remarked that the load acquired such a pro- 

 portion of the large moving force of the water displaced 

 by the ship as the mass of the load bears to the mass of the 

 ship. Thus if 100 tons be employed in a vessel of 1000, 

 the machine acquires 1-lOth of the whole moving force of 

 the water displaced ; this being indirectly abstracted, as Mr. 

 Tower well expresses it, from the vast store of energy 

 passing beneath the feet. In other words, every ton becomes 

 imbued with the force with which the same weight of water 

 — i.e., of thirty-five cubic feet — is moving at the time : in the 

 case of a load of 100 tons consequently representing the 

 energy of 3500 cubic feet of water moving with the speed 

 of the wave motion. The considerable effect of this may 

 perhaps be apparent (though the applications are quite dis- 

 similar) by observing the effect of even a sluggish stream in 

 turning a water-mill. 



The experiments briefly detailed above have been since 

 repeated in different forms with the same results, and have 

 been admitted to have shown the correctness of the method 

 employed, whatever may be the theory of its action, in 

 applying the energy stored in the movements of the sea. 

 As some doubt was expressed at the British Association 

 (Bristol, 1875) as to the ability of the machine to drive a 

 ship against a head sea, Mr. Froude (who was at the time 

 President of the Mechanical Section) stated that he had 

 himself witnessed the model in Torbay driving itself against 

 and through a head sea which, in comparison with the size 

 of the model, was mountainous. As this refers to a point 

 of importance, the testimony of so distinguished an authority 

 may, I think, be regarded as definitive on the matter. A 

 proposition to which value has been attached is that, given 

 the same bulk and weight, the power developed under 

 ordinary circumstances compares favourably with that of a 

 steam-engine, and under exceptional states of the sea it is 

 very much greater. I think I may say that the very care- 

 fully repeated experiments of Mr. Tower do not leave room 

 for doubt on this head. In any case it would appear that, 

 apart from auxiliary propulsion, a useful source of power 

 for many minor purposes at sea exists. As regards pumping, 

 it may be remembered that the power referred to is mostly 

 greatest in those emergencies when it is most required — viz., 

 when a vessel is at the mercy of the elements, and when 

 fires cannot be maintained. 



