MOVING FORCE. 
and it is remarkable, that the cases selected by Mr. IVfaclaurin of diffi. 
- , , . cultv 111 the 
are all of that description. docin. es of 
i^'ar be is from me to say, that the oversights of that excellent “ovuig force, 
philosopher and profound mathematician, or that the omissions 
or oversights of any of the distinguished men to whose woihs I 
have referred, ar^ of much inrportance when compared wiih 
the numerous benefits which they h.ive rendered to science. 
I only wish to show, that the principle which appears to me 
0 be capable of general and correct application. Las been con- 
demned on insufficient grounds ; and the circumstance of such 
1 man as Maclaurin having been led to erroneous conclusions 
)y reasoning from the supposed action of hard bodies, affords 
he best argument for rejecting that doctrine. 
M. D’Alembert appe.ars to have been fully sensible of the 
liffirulties which attend tlie solution of problems of this *de- 
;cription ; and, from his general reasoning respecting them, at 
well as from the demonstrations of some of them which he 
aas given, it is obvious that, without considering the pressure 
and the space through w'bich it acts, as well as the lime of its 
acting during theproCMv, if 1 may so call it, of collision, the 
csulting velocities and directions of the bodies, alter collision, 
.•aniiot be determined. 
I have selected the case which I have slated (as I have selected 
II the rest) as being the most simple of its kind : and the 
olution w'hich 1 have ofiered is also simple ; being derived 
rom examining the pressures and the spaces through which 
tiey act in producing the motion of A. 
The 12th example is stated for the purfxase of showing, that 
11 cases where quantity of motion, in one direction, forms no 
lart of the subject to be considered, there is in the collision of 
ion«elastic bodies, a positive loss of force, in whatever way it 
lay be reckoned ; and if that loss be estimated by examining 
^le pressures and the spaces through which they act, a change 
If figure, corresponding to the force w hich has been expended, 
•ill be found. 
The 13th case was proposed to me by my friend Mr. Dalton, 
I) whose candid encouragement I have been much indebted in 
VoL. XXXVI.— No. i68. T ih* 
