216 C.’s Reply to D. (Serr. 
in his Account of Newton’s Philosophical Discoveries, p. 130, 
“the same laws that serve for comparing, compounding, or 
resolving motions, are likewise observed by pressures ; that is, 
the powers that generate motion or tend to produce it; and it 
adds no small beauty to this theory-ef motion that both observe 
the same laws.” Accordingly many of the laws of collision of 
bodies are afterwards exhibited by Maclaurin from the effects of 
pressure. In formerly observing, therefore, upon Mr. H.’s 
theory, | exhibited the incorrect consequences which were dedu- 
cible from his reasoning on the laws of motion in a sentence 
similar to the corallary just quoted, by an instance of its effect in 
a case of pressure. ‘ Thus if a man push with all his strength 
against a wall, say with a force as 10, action and reaction being 
equal, the wall resists with a force as 10, exactly in a similar 
manner to the fixed plane in Mr. H.’s proposition. If instead of 
the wall there be an opposing active force, another person, for 
instance, pushing agamst the first with an exactly equal force, 
the effect to the first will be just the same as the wall, and neither 
person will be able to move the other. But by Mr. Herapath’s 
reasoning, each person would be acted on ina direction opposite 
to that towards which he pushed, by a force equal to twice the 
force of either one; thatis, with a force as 20; and consequently 
both must be pushed backwards ; a conclusion notoriously con- 
trary to fact. And yet this is the reasoning by which are to be 
overturned, in one short page, the doctrines of Newton, Maclau- 
tin, Hutton, Playfair, and innumerable other mathematicians, m 
relation to the collision of hard bodies; the first principles of 
which too are as nearly as possible self-evident.” Upon this, D. 
‘observes, “‘ These sentences, as far as I understand them, dis- 
tinctly charge Mr. H. with confounding pressure with impulse.” 
Certainly no understanding can be worse than one which chooses 
to misunderstand, and no other could derive such a charge from 
those sentences. He adds afterwards, “ C. tells us that the 
pushing case I have just quoted which (with how much truth the 
reader may judge from the counter quotations), he informs the 
world, is Mr. Herapath’s, is that, by which it is intended by Mr. 
H. that the doctrines of Newton,” &c. “ are to be overturned, in 
relation to the collision of hard bodies.” I will only observe 
upon this, that the extract is all that I ever said on the subject ; 
and it may be thence ascertained whether, when D. said that I 
charged Mr. H. “ with confounding pressure with impulse,” that 
Linformed the world that “ the pushing case,” as he calls it, was 
Mr. Herapath’s, and that I told them it was by that by which it 
was intended by Mr. H. that the doctrines of Newton, &c. were 
to be overturned, his assertion was not absolutely untrue. His 
motive in the assertion may be gathered from his insinuation that 
what I said was not accordant with truth. 
I have now, I believe, examined all that-is offered in the form 
of reasoning in D.’s papers. Had it indeed been reasoning, 
