MINES AND MACHINERY. 
533 
done by a pound, or any other given weight of 
coal consumed in working a steam engine ; since 
the quantity of water that the engine will raise 
to a given height, or the number of quarters of 
corn that it will grind, or, in short, the amount 
of any other description of work that it will do, 
is proportionate to that duty. As the principal 
working of mineral veins can only be continued 
by descending deeper every year, the difficulty 
of extracting metals is continually on the in- 
crease, and can only be overcome by those en- 
in Cornwall, of which Mr. Taylor considers the average duty, 
under ordinary circumstances, to be above 90,000,000; and which 
has been made to lift 97,000,000 lbs of water one foot high, with 
one bushel of coals. 
The effect of these improvements on the operations of mines, 
in facilitating their drainage, has been of inestimable importance 
in extracting metals from depths which otherwise could never 
have been reached. Mines which had been stopped from want 
of power, have been reopened, others have been materially deep- 
ened, and a mass of mineral treasure has been rendered avail- 
able, which without these engines must have been for ever inac- 
cessible. 
It results from these rapid advances in the application of 
coal to the production of power, and consequently of wealth, that 
mining o|)erations of vast importance, have been conducted in 
Cornwall at depths till lately without example, c. g. in Wheal 
Abraham, at 24'2 fathoms, at Dolcoath at 235 fathoms, and in the 
Consolidated Mines in Gwenuap at 290 fathoms, the latter mines 
giving daily employment to no less than 2,500 persons. 
In the Consolidated Mines, the power of nine steam engines, 
four of which are the largest ever made, having cylinders ninety 
inches in diameter, lifts from thirty to fifty hogsheads of water 
per minute, (varying according to the season) from an average 
