1822.] C's Replyto.D. 199 
contact with equal and opposite momenta, they will separate 
after the stroke with the same velocity with which they met.”— 
(Annals, April, 1821, p.285.) 
Sir Isaac Newton says, ‘‘ Bodies which are either absolutely 
hard, or so soft as to be void of elasticity, will not rebound from 
one another, Impenetrability only makes them stop. If two 
equal bodies meet directly in vacuo, they will by the laws of 
motion stop where they meet and lese all their motion, and 
remain at rest; unless they be elastic and receive new motion 
from their spring.” —(Newt. Opera, vol. iv. p. 258.) 
“‘ Non-elastic bodies on their shock will adhere together, and 
either remain at rest, or else move together as one mass with a 
common velocity ; or if elastic, they will separate after the shock 
with the very same velocity with which they met and shocked.” 
—(Hutton’s Math. Dict. in verb. Percussion, p. 215.) 
These propositions from such men as Newton and Hutton (and: 
similar mght be extracted from the writings of Kaclaurin, Play- 
fair, and other philosophers of that rank) will, I hope, justify my 
opinion that Mr. H. did attribute to hard bodies properties 
actually belonging to elastic bodies. It is, however, quite clear, 
that no one could honestly believe those expressions amounted 
to “ an assertion that Mr. H. makes hardness and elasticity the | 
same;” yet so D. in a subsequent part of his paper (Annals, 
May, p. 350) ventures untruly to callit, and that for the purpose 
of making it appear, contrary to éhe fact, that I had asserted 
that which was not true. 
It is, however, most extraordinary that D. in the very moment 
of his attack upon another for a supposed misrepresentation of 
the meaning of Mr. Herapath, should, with all the formality 
with which he has introduced the quotation from his paper, 
misstate his expression. There is in fact no such word as 
“elasticity” in the sentence which D: pretends to quote, he 
having substituted that word for the word “ softness.” Nor, [ 
fear, can we in excess of candour attribute such a strange pro- 
ceeding to accident, or oversight ; since he has by his attempt- 
ing in a note to excuse it, proved that he did it wilfully. It is 
not, however, easy to conceive, what sufficient excuse can 
be made for intentionally giving as. a,quotation from another 
paper that which D. knew at the time was not so. 
Nor was the alteration made to accommodate the sentence 
to Mr. H.’s meaning; for he must have known that Mr. H. did 
not think hardness and elasticity to be ‘‘ 2m direct contrariety:” 
. for in a sentence. the very next to one which D. has quoted on 
this subject, Mr. H. calls elasticity “almost the very opposite of 
hardness ;” and it is evident that what he thought only “ a/most 
the:very opposite,” he could not think to be ‘in direct contra+ 
1 t' 7? 
Dis knowiedge of Mr. Herapath’s real opinion on the subject 
too is proved by his own note; whichis as follows’: ‘‘ Mr. H.! 
