250 Literary and Philosophical Society. 



effect. Ewart then proceeds to the consideration of 

 change of figure. Smeaton, he says, was the first who 

 subjected to actual measurement the force spent in pro- 

 ducing change of figure in the collision of non-elastic 

 bodies. His dissertation, however, has been almost totally 

 neglected by succeeding writers. Of the Illustrative ex- 

 periments brought forward by Ewart one was suggested 

 by Dalton. It is stated in order to show that the same effect 

 is produced by the same fo'rce whether it act by gradual 

 pressure or by sudden percussion. It treats of the impact 

 of a prism fixed at one extremity upon a piece of clay, the 

 impression is the same at whatever distance the clay is 

 placed from the centre of motioft. Ewart thinks 'that 

 great misunderstandings respecting the subject have 

 arisen from the various senses in which the terms have 

 been taken must be acknowledged, but it cannot, I think, 

 be reasonably contended that the whole has been merely 

 a dispute about words.' He also thinks it was a misfortune 

 that the principle of vis viva was brought forward in 

 opposition to the Newtonian doctrine of force. Ewart 

 does not regard it in opposition but rather as an extension. 

 In order to have the history of this measure we must go 

 as far back as Galileo. Mr. Robins and Maclaurin seem 

 to ignore this and regard it as a new doctrine brought 

 forward by Leibnitz and his followers. Ewart says as far, 

 therefore, as the measure of force which is composed of 

 the pressure into the space through which it acts can be 

 applied to the estimation of the force of moving bodies, it 

 is properly speaking the doctrine of Galileo and Newton. 

 The same principle has been still further extended and 

 applied to explain the phenomena of force producing 

 changes of figure in masses of matter. Ewart states ' all 



