. Moving Force. ~ 203 
induction of facts,.it must stand or fall with 
the facts on which it is grounded. 
In the next case, where the angle BAC 
(fig. 11) is not a right angle, the results after 
collision are, in two respects, different from 
the last. Ev and F are not at rest after col- 
lision ; and the quantity of motion of A is not 
the same as that of the common centre of 
gravity of E and F before collision.* This 
case, or rather the converse of it in a less 
simple form, was first explained by Jokn 
Bernoulli in. the eleventh chapter of his 
“« Discours sur le Mouvement,’ and the 
solution which I have given (page 123) will 
be found to agree with his. In his twelfth 
chapter, however, he extends his solution to 
the case where a ball D (fig. 16) strikes any 
number of pairs of balls,—the balls in each 
pair being equal and at equal distances from 
the line of direction of the striking ball.— But 
that solution, as it has been justly observed by 
Mr. Robins, “ will be true only when the 
same time is taken up in communicating 
* In describing this case at page 123, I have omitted to 
state that E and F are supposed.to move with equal veloci- 
ties; but it will be obvious from the figare and from the 
results which are given, that it was so understood, 
1 CaQad 
