Moving Force. 215 
ings. It is probable therefore that I may 
not have understood them, in all instances, in 
their proper, or even in their intended mean- 
ing.* I have been careful however to give, in 
most cases, the authors’ own words; and in 
all cases I have given such references that 
any mistakes of that kind may be easily de- 
tected by those who are disposed to examine 
the subject. 
That great misunderstandings respecting 
the subject under consideration have arisen 
from the various senses in which the terms 
have been taken, must be acknowledged. 
But it cannot, I think, be reasonably con- 
tended that the whole has been merely a dis- 
pute about words. 
Soon after it had been shown by Huygens 
that the “ascensional force” of a body im 
motion is as the square of ‘its velocity ; that 
* Since page 150 was printed, I have noticed that the fol- 
lowing passage (line 17) “that the maximum effect must 
consequently be as AXc*” should be corrected thus ‘that 
the maximum effect of a given quantity of water must con- 
sequently be as c?.” I wish to observe also, that although 
the reviewers admit that there is a great difference between 
* the theoretical conclusions and the acknowledged results 
of experience, they appear to consider the theory to be 
unexceptionable. To that I could reply only by stating at 
some length the difficulties which attend the application 
of the theory to practices 
