THE CORNISH PUMPING ENGINE. 
17 
to the expenditure of fuel, as might naturally be the case from the great cost 
this entailed upon the adventurers, notwithstanding the reduction in the price 
of coals. 
We have but scanty information of the general performance of the engines in 
Cornwall, as regards their consumption of fuel, before Smeaton adapted his im 
provements to them; but we may arrive at a fair estimate by comparison w T ith 
others upon a similar construction whose duty was ascertained. 
Smeaton computed the effect of fifteen fire engines at work at Newcastle in the 
year 1769, and found the average duty 28 of the whole equal to 5,590,000 lbs. lifted 
one foot high by the consumption of one bushel of coal. The greatest w r as 7,440,000, 
the least 3,220,000. 29 
We have, however, an account of a trial of two engines on a mine at Poldice, in 
Cornwall, in 1778, undertaken by a committee for the purpose of future comparison 
with Watt’s engines (see Art. 36). The duty of these was found to be 7,037,0001bs. 
lifted one foot with one bushel of coal. This may probably be a little above the 
average duty for the whole county, but in the absence of positive data, we may take 
7,000,000 as the average duty of the atmospheric engine in this district during the 
period above referred to. 
24. The engines in Cornwall were probably made and attended to with greater 
attention to economy of fuel than at the mouth of coal mines where fuel was so 
much more plentiful, but still the consumption was very great, and various 
attempts were made by the engineers to reduce it. The fire-place was diminished 
and enlarged again ;—the flame was carried round from the bottom of the boiler in 
a spiral direction, and conveyed through the body of the water in tubes before its 
arrival in the chimney ;—some used a double boiler, so that fire might act in every 
possible point of contact;—boilers of granite or “ moorstone ” were proposed and 
tried, 30 having tubes of metal to convey the flame through them, (probably either 
for the sake of economy in the manufacture, or under the impression that the 
external iron surface of the ordinary boiler conducted the heat aw^ay too fast);—and 
endeavours were made to adapt the waste heat from furnaces for smelting and 
28 For an explanation of this term, see Art. 37. It must be observed that this method of estimating 
the performance of engines was not in use at the date here referred to, having been introduced by 
Watt, and Smeaton having expressed it in another form: but from his data the duty has been calcu 
lated, and has been thus given in the text for the sake of uniformity with the subsequent and now 
existing practice. 
29 Farey on the Steam Engine, page 234. 
30 A patent was taken out by the celebrated Brindley, in 1759, for a boiler to be made of wood and 
stone, with a cast iron fire-place within it. 
D