218 C.’s Reply to D. [Supr. 
water always being in favour of the temperature of the water, 
and the excess of magnitude in the particles of mercury by its 
less disposition to be affected in volume by changes of tempera- 
ture.” Thus it appears that Mr. H. pretends to ascertain the 
proportionate number of atoms by the mean temperature of the 
bodies on their mixture, as determined by experiment; and. it 
having been so determined that if a given volume of mercury at 
the temperature of 100° Fahr. be mixed with an equal volume of 
water at the temperature of 40°, the temperature of the mixture is 
about 60°, and consequently that the effect ofthe water upon the 
temperature in proportion to that of mercury is as 2 to 1 nearly, 
that is assumed by Mr. H. to be the proportionate number of 
atoms. Mr.H.then proceeds, “ Taking these numbers for cor- 
rect, I find that if a given volume of mercury at the temperature 
of 100° Fahr. be mixed with an equal volume of water at the 
temperature of 40°, the temperature of the mixture should be 
592°; by Dr. Henry, itis 60°. And if the same temperatures be 
taken, but the water be put at the higher, and the mercury at 
the lower temperature, the mixture should be at 791°: Dr. 
Henry says it is nearly 80°.” Thus it is first assumed that if 
upon the mixture of equal quantities of mercury at 100°, and 
water at 40°, the resulting temperature is 60°, the numeratom, 
as Mr. H. calls it; that is, the proportionate number of atoms in 
the water in comparison with those in the mercury shall be as 
2to1. And the comparison of Mr. H.’s theory with experiment 
consists in reasoning back again, that if the numeratom be as 2 
to 1, then if a given quantity of mercury at 100° be mixed with 
an equal quantity of water at 40°, the resulting temperature 
ought to be nearly 60°. That is, if it be true that if the result- 
ing temperature be as 60°, the numeratom must be as 2 to 1, then 
if the numeratom be as 2 to 1, the resulting temperature shall be 
as 60°. So that if you will tell Mr. H. what will be the result- 
ing temperature of a mixture of two fluids having certain previous 
temperatures, he will by his theory again tell you the very same, 
and will also calculate what wili be the temperature of a mixture 
of the same fluids mingled at other temperatures. This mode 
of reasoning will doubtless give results very accurately coincid~ 
ing with experiments, but as it is merely reasoning in a circle, it 
can tend very little to prove the truth of the theory, however 
long a list may be furnished of such facts. 
Another topic to which D. frequently refers, with much appa- 
rent self gratulation, is the opinions of other philosophers, and 
chiefly that of Sir I. Newton. To him he refers more than a 
dozen times, but only once for the purpose of making a quota- 
tion in confirmation of the theory, and that once he draws an 
inference which the next sentence would have shown was incor- 
rect, and which is directly contradicted by other parts of his 
works. With what justice he claims the support of several 
other philosephical writers to whom he has referred, the extracts 
