Moving Force. 255 



proportional, was the proper measure of the effect of a body 

 in motion. 



The main object of Mr. Ewart's paper, in accordance 

 with the conclusions of Smeatoi) (Phil. Trans. 1776), Dr. 

 Wollaston, and others, was to show that if a constant pres- 

 sure applied by any agent were multiplied by the space 

 through which it acted, the result, being in a given propor- 

 tion to the vis vivay was the most natural measure of 

 moving force. He urged that if the effects of pressures 

 were estimated with regard to the spaces through which 

 they passed, instead of the velocities for a certain time, 

 they would apply, as a measure of work done, in all the 

 cases of practical mechanics ; and would, he contended, 

 remove many inconsistencies and errors from th^ reason- 

 ings upon questions occurring in them. He gives illustra- 

 tions of his statements from almost every branch of practical 

 mechanics and hydraulics ; pointing out discrepancies, and 

 solving various problems according to the principles he had 

 assumed. He compared the conclusions from the common 

 theory of fluids with the results of Smeaton's experiments 

 on water-wheels (Phil. Trans. 1759), arriving at interesting 

 conclusions ; but the more recent investigations on this 

 subject by Poncelet and others, with the very important 

 experiments of the committee of the Franklin Institute, 

 upon wheels of 20, 15, 10, and 6 feet diameter — together 

 with those of M. Morin, on the turbine of M. Fourneyron — 

 have placed all others in the shade. Mr. Ewart made 

 many experiments on the reaction of effluent water, and 

 applied the results of his researches on this subject to the 

 solution of the problem of the recoil engine, known by the 

 name of Barker's Mill. ... 



Mr. Ewart adduces, in his paper, several cases which 



