96 
9. I have next to point out that Mr. Dyer, in criticising 
the 4th Article of my Essay, represents me as making a 
certain statement, commencing as follows — “ It is natural to 
suppose that the motion, during this phenomenon, has not 
been really destroyed,” &c. — in order to account for what he 
calls the “ non-production of heat by the moving force exerted 
in waterfalls.” 
10. Now there does not occur in my Essay one word about 
any such “ non-production of heat,” nor one phrase or allusion 
which by any conceivable amount of ingenuity can be con- 
strued to bear any such meaning. The “phenomenon” 
really referred to in the passage above cited, and distinctly 
described in the paragraph preceding it, is the well established 
fact of the production of heat by the fall of water ; and that 
not as a thing to be accounted for, but as a fact to be reasoned 
from. In this instance my meaning has again been exactly 
reversed in Mr. Dyer’s account of my Essay. 
11. I shall not enter into any controversy respecting the 
theory of heat ; for it appears to me that physical theories 
are questions to be settled, not by argument, but by experi- 
ment and calculation ; and I have nothing at present to add 
to the experiments and ctdculations already published. 
12. My only object in writing this letter is that my brief 
sketch of the mechanical theory of heat, which Mr. Dyer has 
criticised, may be judged according to its real contents, and 
may not be erroneously quoted in a publication so important 
as the Transactions of the Literary and Philosophical Society 
of Manchester * 
I am, Sir, 
Your most obedient Servant, 
W. J. MAC QUO 14N RANKINE. 
Glasgow, 21st March, 1863. 
* Mr. Dyer states that in making the quotations from the Engineer lie 
had studied brevity, and had no thought of conveying any other than Mr. 
Eankine’s meaning. — E d. 
