126 MR. DAVIES GILBERT ON THE PROGRESSIVE IMPROVEMENTS 
Diameter of 
Cylinder in 
inches. 
Duty. 
Observations. 
1 
20 
10’015000 
o 
21 
16’385000 
3 
45 
29’668000 
It was believed at the time that some inaccuracy must have oc- 
4 
36 
28’212000 
curred in the communications respecting these two engines. 
Double 5 
42 
18’193000 
6 
63 
15’190000 
Double 7 
45 
15’180000 
8 
45 
15’571000 
On the same mine. The length of strokes in all but one, six 
9 
45 
15 090000 
feet; in that, eight feet. Average duty of the whole, 15’985000. 
10 
45 
14384000 
Double 11 
42 
18’740000 
12 
42 
15’532000 
13 
36 
18’465000 
14 
— 
12’226000 
The diameter of the cylinder not returned. 
15 
30 
14’050000 
16 
20 
12’366000 
Double 17 
14f 
6’097000 
18 
30 
13’931000 
19 
28 
19739000 
20 
36 
24’514000 
21 
21 
13’215000 
22 
20 
15’034000 
■* 
23 
48 
27503000 
£ 
Supposed to be the best engine. 
17’671000 
The general Average in 1798. 
It may be observed that the average duty was here somewhat less, than it 
had been found in 1793, confirmatory of an opinion generally entertained that 
the steam engines had deteriorated from the time of Mr. Watt’s quitting his 
residence near Redruth. 
The principles and even the mechanism of Mr. Watt’s engines have re- 
mained unaltered since their first introduction, unless a change in the precise 
periods of opening and closing the valves could be considered a variation. 
But to such an extent has the economy of fuel been carried by the use of 
steam at a high degree of temperature and consequently of pressure, usually 
from fifty to sixty inches of mercury above the atmosphere, by extending the 
expansive action to two thirds or even to three quarters of the whole descent 
of the piston, by making small fire-places, with sharper drafts, in iron tubes 
surrounded by the water of the boiler, by more effectually preventing the 
escape of heat, by enlarging the engines themselves, and perhaps by executing 
the work with superior accuracy, that in the monthly return of duty performed 
in Cornwall by the steam engines in December 1829, — the best engine with 
