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 ...

266 THE STEAM ENGINE.
consumption of fuel under marine boilers is less than under
land boilers, in the proportion of 2 to 3 very nearly. On
the other hand, I have ascertained from general observation
throughout the manufacturing districts in the North of England, that the average consumption of coals under land
boilers of all powers above the very smallest class is at the
rate of 15 pounds of coals per horse-power per hour. From
this result, the accuracy of which may be fully relied upon,
combined with the result of the experiments just mentioned
at Soho, we may conclude that the average consumption of
marine boilers will be at the rate of 10 lbs. of coal per horsepower per hour. MIr. Field, of the firm of Maudslay and
Field, in his evidence before a Select Committee of the
House of Commons on Steam Navigation to India, has
stated from his observation, and from experiments made at
different periods, that the consumption is only 8 lbs. per
horse-power per hour. In the evidence of Mr. William
Morgan, however, before the same committee, the actual
consumption of fuel on board the Mediterranean packets is
estimated at 16 cwt. per hour for engines of 200 horsepower, and 8~ cwt. for engines of 100 horse-power. From
my own observation, which has been rather extensive both
with respect to land and marine boilers, I feel assured that
10 lbs. per hour more nearly represents the practical consumption than the lower estimate of Mr. Field. We may
then assume the daily consumption of coal by marine
boilers, allowing them to work upon an average for 22
hours, the remainder of the time being left for casual stoppages, at 220 lbs. of coal per horse-power, or very nearly 1
ton for every ten horses' power. In short voyages, where
there will be no stoppage, the daily consumption will a little
exceed this; but the distance traversed will be proportionally
greater.
When the proportion of the power to the tonnage remains
unaltered, the speed of the vessel does not materially change.
We may therefore assume that ten pounds of coal per horse