')32 POWER OF STEAM ENGINES. 
there is virtue in a bushel of coals, properly con- 
sumed, to raise seventy millions of pounds weight 
a foot high. This is actually the average effect of 
an engine at this moment working in Cornw'all. 
The ascent of Mont Blanc from Chamouni 
is considered, and with justice, as the most toil- 
some feat that a strong man can execute in two 
days. The combustion of two pounds of coal 
would place him on the summit.” 
The power which man derives from the use of 
mineral coal, may be estimated by the duty* 
* The number of pounds raised, multiplied by the number 
of feet through which they are lifted, and divided by the number 
of bushels of coal (each weighing eighty-four pounds) burnt in 
raising them, gives what is termed the duty of a steam engine, and 
is the criterion of its power. (See an important paper on im- 
provements of the steam engine, by Davies Gilbert, Esq. Phil- 
Trans. 1830, p. 121.) 
It is stated by Mr. J. Taylor, in his paper on the duty of steam 
engines, published in his valuable Records of Mininy, 1829 , that 
the power of the steam engine has within the last few years been 
so advanced by a series of rapid improvements, that whereas, in 
early times, tlie duty of an atmospheric engine was that of 
5,000,000 pounds of water, lifted one foot high by a bushel of 
coal, the duty of an engine lately erected at Wheal Towan in 
Cornwall, has amounted to 87,000,000 pounds; or, in other 
words, that a series of improvements has enabled us to extract 
as much power from one bushel, as originally could be done 
from seventeen bushels of coal. Thus, through the instruroen- 
' tality of coal as applied in the steam engine, the power of 
over matter has been increased seventeen fold since the first in- 
vention of these engines ; and increased nearly threefold witbm 
twenty years. 
There is now an engine at the mines called the Fowey Consol® 
