534 WORK DONE BY STEAM ENGINES. 
larged powers of draining which Coal, and the 
steam engine, alone supply. It would be quite 
impossible to procure the fuel necessary for these 
engines, from any other source than mineral coal. 
The importance of Coal should be estimated, 
not only by the pecuniary value of the metals 
thus produced, but by their further and more 
important value, when applied to the infinitely 
varied operations and productions of machinery 
and of the arts. 
It has been calculated that in this country about 
15,000 steam engines are daily at work; one of 
those in Cornwall is said to have the power of a 
thousand horses,* the power of each horse, ac- 
cording to Mr. Watt, being equal to that of five 
and a half men ; supposing the average power of 
each steam engine to be that of twenty-five horses, 
we have a total amount of steam power equal to 
that of about two millions of men. When we con- 
depth of 230 fathoms. The produce of these mines has lately 
amounted to more than 20,000 tons of ore per annum, yielding 
about 2,000 tons of fine copper, being more than one seventh 
of the whole quantity raised in Britain. The levels or galleries 
in these mines extend in horizontal distance a length of about 43 
miles. (See J. Taylor's account of the depths of mines, third 
report of British Association, 1833, p. 428.) 
Mr. J. Taylor further states, (Lond. Edin. Phil. Mag. Jan. 
1836, p. 67) that the steam engines now at work in draining the 
mines in Cornwall, are equal in power to at least 44,000 horses, 
one sixteenth part of a bushel of coals performing the work of a 
horse. 
* When Engineers speak of a 25 horse Engine, they mean one 
