Dr. Bottomley on Ewart. 249 



be its velocity) by merely doubling the number of its floats 

 or planes acted upon by the water. Ewart also objects 

 to some experiments of D'Alembert, Condorcet, and 

 Bossut, as not sufficiently comprehensive and admitting 

 deductions of an arbitrary kind. He mentions some 

 experiments of Don Juan and M. Buat, on the pressure 

 of moving water on planes ; their results do not agree with 

 the ordinary theory. Smeaton's observations on these 

 matters, although neglected by authors, have not been lost 

 to practical men, and have led to the disuse of undershot 

 wheels, which about fifty years ago were more prevalent 

 but are now rarely met with. Smeaton's principle was to 

 apply the water so that it should act more by its weight 

 than by its impulse, an advantage being thereby gained. 

 The Edinburgh Reviewer objects to the opinion of Mr. 

 Smeaton ; allusion is' made to the doctrine of the Carte- 

 sians, which was also maintained by Leibnitz and John 

 Bernoulli, that motion could not be lost, for the same 

 quantity of motion or of force, it was said, must be always 

 preserved in the world. With reference to the principle 

 Ewart states, ' It has never been questioned that motion 

 may be generated, accelerated, or retarded in a variety of 

 ways, and there appears to be no good reason for sup- 

 posing that it may not be destroyed as well as generated/ 

 Ewart then refers to some arguments of Maclaurin's 

 that have always been considered the strongest that have 

 been brought against the principle of vis viva. 



These arguments are contained in a treatise that 

 obtained the prize of the Royal Academy of Science at 

 Paris in 1724. Ewart thinks that Maclaurin and 

 Bernouilli reason from different principles ; he also gives 

 some remarks of Dr. Milner upon the paper to the same 



