MOVING KORCK. 
£47 
aae> or rather the converse of it in a less sinaple form, was Cases of diffi- 
irst explained by John Bernoulli, in the eleventh chapter of 
lis “ Discours sur le Mouvement," and the solution which I moviU' force. 
lave given (page 123) will be found to agree w iilt his. In his 
welfih chapter, however, he extends his solution to the case 
vhere a bill D (tig. IG) strikes any number of pairs of balls, 
he balls in each pair being equal and at equal distances from 
he line of direction of the sttiking ball. But that solution, as 
t has been justly observed by Mr. Robins, will be true only 
vhen the same lime is taken up in t'onimunicaiing motioti to 
dl the balls*,” and that cannot take place unless a peculiar 
nodidcation of the elasticity be adapted to the respective masses 
tod positions of each pair of balls at their points of contact ; 
md even then the results will not always be as they ate laid 
lown by M. Bernoulli, His solution, therefore, was not, 
what he understood it to be, a general one. 
Cases of this description appear to have been imperfectly 
anderstood at the time when M. Bernoulli wTote, In the “ His- 
■oire de I’Academie Royale” of Paris, for the year 1/21. p. 84, 
he following case is stated. Two equal balls moving with 
;qual velocities, are supposed, as in the eleventh case, to strike, 
Lt the same instant, a third ball at rest j and the directions AC 
ind AB of the striking balls E and F, are supposed to be such, 
bat w'e shall have AC or AB = 2 AH. That is, that the 
bbsolute velocity of E or F, before they strike A, shall be equal 
<.o twice the velocity of their cotnmou centre of gravity. And 
tt is concluded, that AD will re[)Tcsent the velocity of A after 
he stroke. 
It appears, also, that some of the most obvious effects of 
I lasticity in the collision of bodies were as much misapprehended 
."hen as the motion of the bodies after collision. In the same 
1-epartment of the valuable work last quoted, for the year 
I 728, the same subject (sur la force des corps cn mouvement) 
’» resumed, and at page 77 there is the following statement. 
“ Un corps, qui a une vitesse ^ parcourir d'un mouvement 
* Koblu's Tracts, vol. 3. p. tS6, 
uniforme 
