Moving Force. 207 
elastic ones,* and it is. remarkable that the 
cases selected by Mr. Maclaurin are all of + 
that description. 
Far be it from me to say that the oversights 
of that excellent philosopher and profound 
mathematician, or that the omissions er over- 
sights of any of the distinguished men to 
whose works [ have referred, are of much 
importance when compared with the nume- 
~ rous benefits which they have rendered to 
science. I only wish to show that the prin- 
ciple, which appears to me to be capable of 
general and correct application, has been 
condemned on insufficient grounds; and the 
circumstance of such a man as Maclaurin 
having been led to erroneous conclusions by 
reasoning from the supposed action of hard 
bodies, affords the hest argument for rejecting | 
that doctrine. . 
M. D’Alembert appears to have been fully 
sensible of the difficulties which attend the 
solution of problems of this description; and 
from his general reasoning respecting them, 
as well as from the demonstrations of some of 
them which he has given, it is obyious that, ~ 
without considering the pressure and the space 
through which it acts, as well as the time of 
its acting, during the process, if I may so 
* Traité de Dynamique, p, 234—5. 
