S Mr Watt on the Origin of Ms ImproveTnents 
prised of his design, I might at least have prevented the errors 
respecting the facts in which I was concerned ; but, upon the 
whole, it is more surprising to me that his recollection should 
have served him so well in narrating transactions of thirty years 
standing, than that it should sometimes have led him astray. If 
I had not retained some memorandums made at the time of, or 
soon after, their occurrence, I should myself have felt great dif- 
ficulty in recalling to mind the particulars at the period when I 
first perused those articles, which was some time after their pub- 
lication. I had about that period an opportunity of personally 
stating to Dr Robison some remarks upon them, of which he 
availed himself to a small extent in the Supplement to the En- 
cyclopaedia Britannica, and probably would have done so still 
more, had he been called upon to remould these articles. 
I have endeavoured to throw most of my corrections into the 
form of notes ; but in some places I judged it necessary to alter 
the text ; which alterations I have marked to be printed in Ita- 
lics, that they may be readily distinguished from the original. 
In a few places I have cancelled part of the text without any 
substitution, none appearing to me to be required. In others I 
have left part of the reasoning unaltered which I did not concur 
in ; as in mere matters of opinion, where no manifest error was 
involved,. I did not conceive it proper to introduce my own spe- 
culations. 
As the subjects of Steam, and Steam-Engines, had been al- 
most dismissed from my mind for many years previous to my 
undertaking this revision, I have called in the aid of my friend 
Mr John Southern, and of my son, whose daily avocations in 
the manufacture of steam-engines, render them more conversant 
with some points, to direct my attention to them ; and of the 
former, to examine such of the algebraic formulae as appeared 
essential,, an office for which he is much better qualified than 
myself ; and he has accordingly marked those formulae with his 
initials. 
f I have not attempted to render Dr Robison’s memoir a com- 
plete history of the Steam-Engine ; nor have I even given a de- 
tailed account of my own improvements upon it. The former 
would have been an undertaking beyond my present powers, 
and the latter must much have exceeded the limits of a com- 
mentary iqx)n my friend’s work. I have therefore confined my- 
