204 On the Measure of 
motion to all the balls,’ * and that cannot 
take place unless a peculiar modification of 
the elasticity be adapted to the respective 
masses and positions of each pair of bails at. 
their points of contact; and even then the 
results will not always be as they are laid 
down by M. Bernoulli. His solution :there- 
fore was not, what he i WO it to be, a 
general one. 
Cases of this description appear to have 
been imperfectly understood at the time when 
M. Bernoulli wrote. In the “ Histoire de 
¥/Academie Royale” of Paris, for the year 
1721, p. 84, the following case is’ stated. 
Two equal bails moving with equal velocities 
are supposed, as in the 11th case, to strike at 
the same instant a third ball at rest ; and the 
directions AC and AB of the striking balls E 
and Fare supposed to be such that we shall 
have AC or AB=2 AH. That is, that the 
absolute velocity of E or F, before they strike — 
A, shall be equal to twice the velocity of 
their common centre of gravity.—And it is 
concluded that AD will represent the velocity 
of A after the stroke. 
It appears also that some of the most ob- 
* Robins’ Tracts, vol. 2. p. 186. 
