Dr. Bottomley on Ewart. 247 



of bodies revolving round fixed axes. Attwood thinks that 

 neither of the measures of force is capable of general 

 application, and also that theoretical views of force have 

 had little effect on the construction of machinery, owing 

 their origin and improvement to long experience of re- 

 peated trials. Ewart demurs to this ; neither does he 

 think that Attwood is supported in his opinion by the 

 history of useful discoveries in machines, giving us ex- 

 amples of men who were both scientific and ingenious, 

 Huygens and Hooke. Smeaton also availed himself of. a 

 just theory in applying water to the best advantage as 

 a moving power. Ewart then proceeds to state some of 

 the difficulties which have occurred to himself and others 

 in the application of the common doctrine of moving 

 force, and describes some particular instances where the 

 difficulties occur, and gives from approved writers on 

 mechanics such observations as appear to have been given 

 in explanation of the points in question. He then gives 

 several examples of force producing motion in bodies 

 from a state of rest, also examples of motion destroyed 

 and of motion transferred from one body to another. He 

 expresses his disappointment that Emerson does not 

 give that information which one might have expected 

 from his analytic skill. Emerson even thinks that vis viva 

 ought not to pass for a principle in science. Attwood 

 points out where Emerson, in the solution of a problem, is 

 led into error by a neglect of this very principle. Some 

 mathematicians have regarded the question of momentum 

 or vis viva as a measure of moving force as a dispute 

 about words. Ewart quotes Prony to the effect. Dr. 

 Milner of Cambridge contends that the dispute is not 

 merely verbal. Dr. Wollaston thinks that the conception 



