MancJiestcr Memoirs, Vol. x/vi. {igoi), No. 10. 1/ 



The members of this Society, as might have been 

 expected, would not look with indifiference upon a dispute 

 which affected so vitally the foundations of mechanical 

 science. Thus we find in Vol. VII. of the Memoirs a paper 

 which was read before the Society by Peter Ewart (1808), 

 wherein the Leibnitzian measure of moving force is 

 supported with great ability. So highly did Dalton 

 estimate the value of this paper that he dedicated to its 

 author the second edition of his Neiv System of Chemical 

 Philosophy, " on the score of friendship, but more especially 

 for the able exposition and excellent illustrations of the 

 fundamental principles of mechanics in his essay on the 

 measure of moving force." Ewart expresses in his paper 

 his indebtedness to Dalton for proposing an experiment 

 in order to show that the same effect is produced by the 

 same force, whether in act by gradual pressure or by 

 sudden percussion, in accordance with Newton's second 

 law of motion which has been so persistently ignored by 

 the zealous advocates of the Cartesian measure of force. 



The continuity of ideas developed by this Society in 

 favour of the Leibnitzian measure of force is further seen 

 in Joule's determination of the mechanical equivalent of 

 heat, by which the temperature of one pound of water is 

 raised i'' F. by the fall of one pound weight through a 

 space of 772 feet, or 772 lbs. from a height of one 

 foot, irrespective of the time of the falling weight. That 

 Joule was an uncompromising opponent of the Cartesian 

 measure of force is evident from his having headed his 

 classical paper on the mechanical equivalent in the 

 Philosophical Transactions with the quotation from 

 Leibnitz that " The force of a moving body is proportio7ial 

 to the square of its velocity or to the height to ivhicJi it 

 would rise against gravity T 



Several interesting illustrations of the principle of vis 



