1822.) C.’s Reply to D. he 
assertion which is wholly untrue, and does me the injustice of so 
estimating my conduct by his own, as to think that meanness 
sossible to me, of which he has shown himself so capable. 
D.’s next proposition is so entirely founded upon the first as 
to require no particular notice, but in order further to confirm 
them both, he makes quotations from Hutton, Playfair, and 
Emerson, which, he says, are “ perfectly compatible ” with his 
theory. That this is true can be easily imagined, as no one will 
doubt that there are many sentences in those authors which, 
having little or no relation to the question, cannot be said to be 
incompatible with it. Thus from Playfair, “ Bodies that have 
equal quantities of motion have equal forces or equal powers to 
produce motion.” But the question here is not whether they 
haye equal powers when their whole power is exerted, but whe- 
ther when the body struck yields to the blow, the whole motior 
is communicated; that is, whether the whole power is actually 
exerted. Again, “the velocities being equal, a double mass will 
strike with a double force, a triple with a triple force, and so on.” 
(Hutton’s Courses, vol. ii. p. 132.) But what has this to do with 
Mr. H.’s proposition, “that the velocities of the moving bodies 
have no effect on the intensities of the strokes” But his refex- 
ence to Maclaurin is more singular. “‘ Maclaurin’s Fluxions,” D. 
says, “in which I believe his views of collision are expounded, 
I have not by me. If I had, 1 should probably be able to give 
another amusing specimen of C.’s knowledge of names instead of 
things.” If D. will refer to Maclaurin’s “¢ Account of Newton’s 
Philosophical Discoveries,” p. 184, et seq. he will find that he 
maintains “thatin the actions of perfectly hard or inflexible bodies 
upon one another,” “as there is no spring nor any force to sepa- 
rate them, they must go on together after their collision as if 
they formed one body.” 
It would, however, be endless to make extracts to this 
effect from all the other writers referred to; 1 have already 
done so in relation to some of them. But it is evident from 
other statements in his paper, that D. knows the fact that 
every one of these authors from whom he has made these quota- 
tions, do, in their works, state propositions in relation to the very 
point in question, directly contradictory to his theory, yet upon 
these quotations alone, D. in effect assumes, what he must know 
to be perfectly untrue, that Playfair and Hutton do not maintain 
those laws of collision of hard bodies which I have attempted to 
support.” (Annals, May, 1822, p. 368.) 
his, however, is not the only disingenuous use he makes of 
these quotations, as will appear from the next extract, which 
contains 2 difficulty or paradox, as he calls it, which, as he states, 
has perplexed him alittle. ‘‘ Let a perfectly hard ball A, mov- 
ing with any velocity a, strike in the line of its motion another 
perfectly hard ball B at rest, then, by the old theory, the motion 
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