1822.] C’s Replyto Do 203 
truth is not merely analogy ; they are still more strongly con- 
firmed by the soundest mathematical demonstrations, and the 
ablest observations of astronomy. But the assertion possesses 
as little trath as modesty. I have already given one instance 
in which Mr. Herapath directly opposes Newton, where 
there is no relation to the reciprocal attraction of the planets ; 
and as it respects the laws of the collision of hard bodies, itis a 
disagreement on the very basis of Mr. H.’s theory. And in 
addition, in the same paper from which D.’s extracts are taken, 
and to which almost the whole of his cbservations relate, Mr. 
H. does himself refer in terms to Newton’s Cor. 5, of the third 
law of motion, and there expressly attempts to controvert it, and 
to prove that it is not true in cases of the collision of unequal 
hard bodies.—( Annals, April, 1821, p. 2.) 
« But,” says D. “since C. opposes Newton to Mr. H. I beg 
to ask him on what grounds he does it? Is it on the doctrine of 
heat?” And he then continues for the purpose of declamation, 
pretending to believe that 1 opposed Mr. H. to Newton upon 
that ground, although in the only two sentences in my paper in 
which Newton’s name is mentioned, the subject of opposition is 
expressly mentioned to be “ the doctrines of Newton in relation 
to the collision of hard bodies,” and for the fact of that opposi- 
tion, | have Mr. H.’s own authority. 
D. after such introductory observations, proceeds “to examine 
the objections to the theory of heat by motion,” nor will the 
examination disappoint the promise of such an introduction. 
The first objection which he attempts to answer, is, where it 
is shown that consequences necessarily arising from the theory 
are contradicted by experiment; whence it is concluded that 
the theory itself cannot be correct. It will not be necessary to 
go through the reasoning to understand the kind of answer 
which is given to it. It was said by me in the course of the 
argument, “ if one atom a, of the body A, having a greater velo- 
city than 6, of the body B, overtake the slower atoms, the atom 
a will lose some of its velocity, which will be communicated to 
the atom 6, and thence among the other atoms of the body B. 
The communication of motion from the atoms of A to the atoms 
of B will not be compensated; for the atoms of B having less 
velocity than the atoms of A, will never overtake them. The 
motion of the atoms of B, therefore, will be increased. So that 
if one body A have atoms of a less magnitude than a body B’ 
with which it is im contact, but with a velocity inversely greater 
(that is, according to Mr. H. the bodies A and B being of the’ 
same temperatures), the momentum of the atoms (that is, the 
temperature of the body B) shall continually increase.” D: 
having’ extracted the greater part of this proposition, says, 
“©What becomes of the temperature of A? I do not know; C. 
has'not told us; but I suppose as the temperature of B shall 
continually increase, that of A increases too.” It must be remem+ 
