86 
MOVING rORC£. 
Casrsof diffi- both instances, the striking forces, if measured by the masses) 
cniiyiiithe into their velocitiesy. are the same; and as the striking balls ( 
doctrines of ' ’ ° ; 
moving force, are in both instances brought to rest, they must have com-) 
municated exactly their whole force to the mass which, was) 
struck. The results, however, are far from being equal. If 
the force of D be no greater than that of C, we shall have 
the rotatory motion produced without force, although we have 
no reason to suppose that the rotatory can be produced with 
less force than the rectilinear motion. ^ ' 
In order to avoid unnecessary calculations or analyses, I have 
stated these cases in the most simple forms I could devise. I 
am aware, that there are many who think they may be easily 
solved in the usual way, and that some of the cases will be 
considered as trivial paradoxes. But if we examine the ex- 
planations which have been given of similar cases, we shall 
find that there is considerable diversity of opinion about the 
V principles by which they are to be explained; and that some 
of the solutions are not quite so obvious as, at first sight, they 
» appear to be. 
Before we enter upon the examination of these particular 
cases, it may be proper to observe, in addition to what has been 
already noticed, that, in respect to the general question, or in 
respect to the existence even of any question at all on this sub- 
ject, some of the best recent authorities are the most difficult 
to be reconciled with each other. 
Few authors, in our language, on the principles of mecha- 
nics, have been more generally read and referred to than Emer- 
son. From the great analytical skill of this author, one would 
have expected something decisive on the long-pending ques- 
tion concerning the measure of moving force ; but he seems 
to take for granted, that the measure is the mass into the velo- 
city or the momenium, for he scarcely condescends to mention | 
the other, and, aft^r a few observations, dismisses it in the S 
j 
following laconic manner. “ It seems to be a necessary pro- f 
perty of the vis viva, that the resistance is uniform. But there 
are infinite cases where this does not happen ; and, in such cases, t 
this law of the vii VIVO must fail. And since it fails in so' 
many j 
i 
i 
