Till'] WATT AND THK THKV1TJIICK KN< JINKS. 177 



increased pressure of steam to the Cornish engines, his 

 friend Davies Gilbert reported the average duty of the 

 Watt engine in Cornwall to be seventeen millions. 



In August, 1811, the reported duty averaged 15*7 

 millions. This was the month and year in which 

 Trevithick, after twelve years of working evidences of 

 the reasonableness of his promises of increased power 

 and economy from using high-pressure steam, was 

 allowed to erect his cylindrical boilers for the large 

 pumping engines in Dolcoath Mine. 



Has the reader realized that the 45-inch atmospheric 

 Carloose engine, of nearly 100 years before, 1 had in 1775 2 

 become the Bullan Garden engine of Trevithick, sen., 

 which was improved and re-erected by Trevithick, jun., 

 in 1799, 3 when the name was again changed, this time 

 to Shammal, because it was linked to another engine, no 

 other than the Watt 63 -inch double engine? This 

 Shammal 45-inch took steam from the globular boiler, 

 using a pole air-pump 4 and a Watt condenser, though 

 retaining the beam with the arched head and chain 

 connection; and again in 1811 took still more highly 

 expansive steam from the cylindrical boilers with a 

 new beam and parallel motion, enabling it in 1814 to 

 beat its rival, the Watt Dolcoath great double engine. 5 

 The old 63-inch Gons, under the name of Dolcoath 

 Stray Park engine, with Trevithick's improvements, did 

 sixty-seven per cent, more work than the Watt 63-inch 

 with an equal quantity of coal. 



This startling fact was disbelieved by the advocates 

 of low-pressure steam, and as the visible change in the 

 Dolcoath engine from Newcomen to Watt, and from 

 Watt to Trevithick, had been gradual and not very 



1 See vol. i., p. 21. 2 See vol. i., p. 25. 3 Sec vol. ii., p. 120. 

 4 See vol. ii., p. 122. 5 See Lean's report, vol. ii., p. 175. 



VOL. II. N 



