THE CORNISH PUMPING ENGINE. 
21 
31. The success of these trials induced the rapid adoption of the improved 
engine, and rendered Cornwall the richest field of profit to the patentees; for in 
about twelve years the whole of the atmospheric engines in the district had been 
replaced by patent ones, 39 whose dimensions varied from 24 to 66-inch cylinders, 
and many of which were double-acting. The extension of the mining operations 
kept up a constant demand upon the manufacturers of the engines, either for new 
machines, or for enlargements of the old ones, which lasted, with only one or two 
temporary interruptions, until the year 1800, when the monopoly expired, and the 
connection of Messrs. Boulton and Watt with the county entirely ceased. 
32. The changes Watt made in the construction of the pumping engine rendered 
it almost a new machine. To describe them all would be as tedious as it is unne 
cessary ; for as Watt’s name stands deservedly first in order of pre-eminence among 
the improvers of the steam engine, it has been naturally the especial care of all 
writers on the subject to give the description of his inventions the most prominent 
place in their works. 40 It will therefore be sufficient for our present purpose simply 
to enumerate the principal of those important improvements, which, as introduced 
into the Cornish Pumping Engine, were productive of so much advantage to the 
county, and rendered the machine so much more efficient than it had ever been 
before. 
They may be said to consist of— 
1st. The preservation of the steam cylinder continually at a high temperature, 
by surrounding it with a jacket of steam, enclosing the whole in a casing of a 
slow heat-conducting material, 41 and doing away with the necessity of intro 
ducing water or other substance colder than the steam therein. 
2nd. The great and important invention of condensing the steam in a separate 
vessel. 
3rd. The removal of the uncondensed air or vapour by the air pump. 
39 Farey on the Steam Engine, page 383. 
40 The most complete and detailed account of Mr. Watt’s inventions is contained in Mr. Farey’s work, 
already alluded to. 
41 Brindley seems to have anticipated Watt in some measure as to the cylinder casing, probably, how 
ever, unknown to the latter. “ In one instance, he (Brindley) surrounded his metal cylinders with a 
wooden case, and the interval was filled with light wood ashes; and by this, and using no more injection 
than was necessary for the condensation, he reduced the waste of steam to almost one-half.”—Rees’s 
Cyclopaedia. Art. Steam Engine. 
In one of Watt’s first engines (that at Ting-tang, mentioned in the last Article,) a small fire was put 
beneath the cylinder to keep it a high temperature, but this was not afterwards practised. The attempt 
was renewed at Binner Downs at a later period, and again laid aside.