MOVING FORCE. 
253 
figure of D, one-elghlh will have produced the progressive Cases of dilfi- j 
motion of G, and one-eighth the rotatory motion of A and B. J 
But if these effects must be estimated by the product of the force- 
mass into its progressive velocity, the change of figure, as well ' 
as the rotatory motion, must be left wholly unaccounted for. 
If the more complicated cases of this description, where *, 
the force is neither communicated in the directions of the cen- ! 
tres of gravity, nor in those of the centres of gyration be ex- 
amined on the same principles by which 1 have attempted to fi 
explain the fifth case, and the case before us, it will be found, 
that the force expended in producing change of figure, added to 
that which is exhibited in the motion of the bodies after col- 
lision, will always be equal to the original force of the striking 
body. 
Having stated, more fully, perhaps, than is consistent with 
the due limits of a paper of this kind, various opinions and 
explanations relating to the examples of force which I have 
oftered to the consideration of this society, I wish to ob- 
serve, that the terms pressure, force, moving force, momentum, 
&c. are used by different authors, and sometimes even by the 
same author, with various meanings. It is probable, therefore, 
that I may not have understood them, in all instances, in their 
proper, or even in their intended, meaning*. I have been care- 
ful, however, to give, in most cases, the authors’ own w’ords ; 
and in all cases I have given such references that any mistakes 
of that kind may be easily detected by those who are disposed 
to examine the subject. 
• Since page loO was printcil, I have noticed, that the following 
pas.sagc (line 17 ) “ that tlie niaxiimiiii etlcct must consefpieiitly be as 
A X c*" sitoiild be corrected thus, “ that tiie maximum effect of a given 
quantity of water must consequently be as c*. I wish to observe, also, 
that, although the reviewers admit that t'lcre is a great difference be- 
tween the tlieoretical conclusions, and the acknow ledged results of ex- 
perience, they appear to consider the theory to be nncxceptionable. 
To that I could reply only by stating, at some length, the difficulties 
which attend the application of the theory to practice. 
That 
