xlvii 
From the period of his experiments with steam of great ten- 
sion, in the high-pressure winding-engine at Dolcoath, in 1806, 
Trevithick sought to use highly-elastic steam in Watt’s condensing 
engine ;* but no opportunity for doing so offered until 1811-1812. 
At that time, however, he erected at Wheal Prosper (Gwithian) - 
an ordinary single-acting condensing-engine of twenty five inches 
cylinder, furnished with his cylindrical, tubular-boiler, in which 
he worked steam of more than forty pounds on the inch; ex- 
panding it,—when the engine was set up—fully seven-eighths of 
the working-stroke.} 
At Doicoath a single-acting condensing-engine,—which had 
been worked by Trevithick in 1800,—performed in February 
1814, when Jeffery and Gribble had become the superintendents, 
the then unexampled duty of 35, millions per bushel,t or—if as 
of late the bushel be taken to weigh 94 lbs.§—41-7 millions per 
hundred weight, of coal. 
Woolf, who had been already engaged by Trevithick as an 
engine-fitter in Cornwall, was—about 1802—sent, by his em- 
ployer, in the same capacity, to London; where—towards the 
latter part of 1803||—he established himself on his own account 
as an Engineer. About the same time he propounded—as estab- 
lished ‘“‘by actual experiment,”—a theory utterly at variance with 
the laws long previously known to govern the dilatation of all 
* Letter of 18th February, 1806, to Davies Gilbert, Esq. Pour, Cornish 
Pumping Engine, pp. 162-163. 
+ Henwood, Phil: Mag: and Annals, x., p. 98. Pole, Cornish Pumping 
Engine, pp. 51-52. 
' + Lean, Historical Statement, pp. 20, 31. 
§ During experiments made in 1831 all the coal used was both weighed 
and measured, and portions from every bushel were afterwards dried by 
the means of a water-bath. The weights when delivered at the boiler-house, 
and after having been dried were at 
Wheal Towan, at the boiler-house 100 lbs., when dried 93-8 lbs. per bushel. 
Binner Downs, 5 92°6 ,, 9p 83-4 ,, ” 
Hast Crennis, ”9 88°3 ” ” 84-1 oo) ” 
Mean .... he 93-6 ,, 45 Sigler. 99 
Henwoop, Trans: Inst: Civil Engineers, ii., p. 58. 
In 1835 a bushel of coal was weighed at the Fowey Consolidated Mines and 
found to be 94 lbs. 
Lean, Historical Statement, p. 99. 
‘*T saw 94 Ibs. (a Cornish bushel) of coals weighed.” 
WicxsteeD, Trans: Inst: Civil Engineers, ii., p. 61. 
|| Trevithick’s account-books (which still exist) show, that in 1803, 
Woolf was paid at the rate of Thirty Pounds a year only. 
