The steam engine familiarly explained and illustrated; with an historical sketch of its invention and progressive improvement; its applications to navigation and railways; with plain maxims for railway speculators. By the Rev. Dionysius Lardner ... With additions and notes by James Renwick ...

DUTY OF ENGINES. 305
given rise to some doubts as to the correctness of the experiments on which the report was founded, it was agreed that
another trial should be made in the presence of a number of
competent and disinterested witnesses. This trial accordingly took place a short time since, and was witnessed by a
number of the most experienced milning engineers and agents:
the result was, that for every bushel of coal consumed under
the boiler the engine raised 125- millions of pounds weight
one foot high.
(141.) It may not be uninteresting to illustrate the amount
of mechanical virtue, which is thus proved to reside in coals,
in a more familiar manner.
Since a bushel of coal weighs 84 lbs. and can lift 56,027
tons a foot high, it follows that a pound of coal would raise
667 tons the same height; and that an ounce of coal would
raise 42 tons one foot high, or it would raise 18 lbs. a mile
high.
Since a force of 18 lbs. is capable of drawing 2 tons upon
a railway, it follows that an ounce of coal possesses mechanical virtue sufficient to draw 2 tons a mile, or 1 ton 2 miles,
upon a level railway.*
The circumference of the earth measures 25,000 miles. If
it were begirt by an iron railway, a load of one ton would
be drawn round it in six weeks by the amount of mechanical
power which resides in the third part of a ton of coals.
The great pyramid of Egypt stands upon a base measuring
700 feet each way, and is 500 feet high; its weight being
12,760,000,000 lbs. To construct it, cost the labour of
100,000 men for 20 years. Its materials would be raised
from the ground to their present position by the combustion
of 479 tons of coals.
The weight of metal in the Menai bridge is 4,000,000 lbs.,
* The actual consumption of coal upon railways is in practice about eight
ounces per ton per mile. It is, therefore, worked with sixteen times less effect
than in the engine above-mentioned.
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