26 
THE CORNISH PUMPING ENGINE. 
was nearly trebled by Watt’s improved engines, the average duty of which was 
seventeen to twenty millions. 
In 1793, an account was taken of the work performed by seventeen engines on 
Watt’s construction, then working in Cornwall. This statement is not verified by 
an authentic report, but there does not appear to be any reason for doubting its 
correctness. The average duty was 19,569,000 lbs. of water raised one foot high by 
the consumption of one bushel of coal. 50 
In 1798, the duty was considerably less, for in consequence of a dispute which 
arose as to the performance of the engines, and which was referred to a committee 
of five persons to decide, (see Art. 54,) the duty of twenty-three engines, four of 
them double-acting, was taken, and the average (excluding two which were supposed 
incorrect) found to be 15,782,000. 
The following is the list of the engines, 51 giving the duty of each, and the 
respective diameters of their cylinders. 
Diameter of 
cylinder in inches. 
Duty. 
Observations. 
20 
10,015,000 
21 
16,385,000 
45 
36 
29,668,000 
28,212,000 
' It was believed at the time that some in 
accuracy must have occurred in the com 
munications respecting these two engines. 
Double 
42 
18,193,000 
63 
15,190,000 
Double 
45 
15,180,000 
On the same mine. The length of stroke 
45 
15,571,000 
in all but one, 6 feet, in that, 8 feet. 
45 
15,090,000 
Average duty of the eight engines, 
45 
14,384,000 
15,985,000. 
Double . . 
42 
18,740,000 
42 
15,532,000 
36 
18,465,000 
12,226,000 
The diameter of the cylinder not returned. 
30 
14,050,000 
20 
12,366,000 
Double 
14f 
6,097,000 
30 
13,931,000 
28 
19,739,000 
36 
24,514,000 
21 
13,215,000 
20 
15,034,000 
48 
27,503,000 
Supposed to be the best engine. 
The best engine of these (excluding the two doubtful ones), which is supposed 
also to be the best recorded during Watt’s time, was one erected at Herland Manor 
mine, said to be performing regularly twenty-seven millions. 52 It was particularly 
50 Phil. Trans. 1830. Paper by Mr. Davies Gilbert. 51 Ibid. 
52 In Robison’s Mechanical Philosophy, page 145, the author remarks, “ The burning of one bushel of