4 Mr Watt on the Origin of his Improvements 
Watt of Birmingham, then of Glasgow, his improvement out 
this useful engine,” (meaning the steam-engine, of which he i^ 
then speaking). There can be no doubt, from what follows in 
his description of the engine, and from the very honourable men- 
tion which he has made of me in various parts of his Lectures,; 
that he did not mean to lessen any merit that might attach to 
me as an inventor ; but, on the contrary, he always was dispos- 
ed to give me fully as much praise as I deserved. And were 
that otherwise doubtful, it would, I think, be evident from the 
following quotation from a letter of his to me, dated 13th Fe- 
bruary 1783, where, speaking of an intended publication by a 
friend of mine on subjects connected with the history of steam^ 
he says, I think it is very proper for you to give him a short 
account of your discoveries and speculations, and particularly^^ 
to assert clearly and fully your sole right to the honour of the 
improvements of the Steam-Engine and in a written testimo- 
nial which he very kindly gave on the occasion of a trial at law 
against a piracy of my invention, in 1796-7, after giving a short 
account of the invention, he adds^ Mr Watt was the sole in^ 
ventor of the capital improvement and contrivance above men-^ 
turned.'^ Under this conviction of his candour and friendship^ 
it is very painful to me to controvert any assertion or opinion of 
my revered friend ; yet in the present case I find it necessary 
to say, that he appears to me to have fallen into an error, and I 
hope, in addition to my assertion, to make that appear by the 
short history I have given of my invention in my notes upon 
Dr Robison’s essay, as well as by the following account of the 
state of my knowledge previous to my receiving any explana- 
tion of the doctrine of Latent Heat, and also from that of the 
facts which principally guided me in the invention. 
It was known very long before my time, that steam was con- 
densed by coming into contact with cold bodies, and that it com- 
municated heat to them. Witness the common still, &c. he. 
It was knowm by some experiments of Dr Gullen, and othersy^ 
that water and other liquids boiled in vacuo at very low heats ; 
water below 100°. 
It was known to some philosophers, that the capacity or equi- 
librium of heat, as we then called it, was much smaller in mer- 
cury and tin than in water, 
s 
