xlv 
engine.* The patentees having been paid in proportion to the 
saving of fuel they effected, the strictest economy was practised 
by their representatives; on their retirement, however, this rigour 
was abated, the engine-men became less careful of their coal, and 
the duty of the engines declined.t For some time, indeed— 
The average did not exceed 14 millions per bushel, 
: \ of coal consumed, 
or 18-6 millions per cwt.........--.eee--eeee:s 
And in rare instances a duty of 6 millions per bushel, Br leoal F 
Oye Sh) vamulbioyng fae Gwk, Gado Goocooodcs0cuco a lag erear Shean 
only, was accomplished. The waggon (hearse) boilers, then in use, 
would have been unsafe with steam of the force commonly em- 
ployed now; and the fires—unlike those recommended by Smeaton 
at Chacewater {—were several feet thick.§ Boulton and Watt had, 
indeed, worked their engines expansively, but Watt himself— 
aware, possibly, of the madequacy of his boilers—had refrained 
from using steam of high tension.|| Nor, in fact, was the pres- 
sure, prevalent throughout the County very materially increased 
during several subsequent years ; for engines set up at the United- 
mines4] by Hornblower, about 1811-1812, were worked in 1821 
by steam which, in the boiler, was balanced by a column of water 
some twenty-two feet in height.** 
The works of Dolcoath, which had been suspended in 1788, 
were resumed in 1800,{} when Trevithick was appointed the 
(mechanical) engineer. From that—if not from an earlier— 
period he conducted the experiments, and devised the various 
forms of construction, which, in 1811,{+ eventuated in the cylin- 
* Henwood, Edin: Journal of Science, x., p. 34. Taylor, Records of 
Mining, i., p. 154. Lean, Historical Statement, p. 8. Pole, Cornish Pumping 
Engine, p. 43. ; 
; Carne, Cornwall Geol: Trans: iii., p. 58. Henwood, Hdin: Journal 
of Science, x., p. 34. Lean, Historical Statement, p. 8. Pole, Cornish 
Pumping Engine, p. 43. 
+ Farey, Steam-Hngine, p. 191. 
-§ Héron de Villefosse, de la Richesse Minérale, i., p. 293. Henwood, 
Edin: Journal of Science, x., p. 35. Pole, Cornish Pumping Engine, 59. 
|| The late Mr. William Wilson (son of Boulton and Watt’s financial 
agent in Cornwall) was present when—some one mentioning the high ten- 
sion at which Trevithick worked his engines—Mr. Watt remarked ‘I could 
have my engines worked to one hundred pounds on the inch; but I—[{would 
not |—be the engine-man.” 
q Lean, Historical Statement, pp. 28, 53. 
** Farey, Phil: Mag: and Annals, viii., p. 309. 
++ Rule, Cornwall Geol: Trans: viii., p. 146. Thomas, (C.), Ibid, p. 
447. 
tt Mr. Francis Trevithick, MS. (Extracted from his Father’s papers). 
‘Phillips and Darlington, Records of Mining and Metallurgy, p. 87. 
