power which would draw 110 tons
upon a railway at a speed of 30 miles an hour, if there were no atmospheric
resistance. The atmospheric resistance is at the rate of 12 lbs. a ton,
with a load of 110 tons, equal to 1,320 lbs., moving at a speed of 30 miles
an hour, which, when reduced, becomes 105.8 horses power, and this, added
to 97.3, makes 203.1, instead of 200 horses power, as ascertained by a
reference to the evaporative power of the boiler. This amount of
atmospheric resistance, however, exceeds the average, and in some of the
experiments for ascertaining the atmospheric resistance, a part of the
resistance due to the curves and irregularities of the line has been
counted as part of the atmospheric resistance.

498. _Q._--Is the resistance per ton of the engine the same as the
resistance per ton of the train?

_A._--No; it is more, since the engine has not merely the resistance of the
atmosphere and of the wheels to encounter, but the resistance of the
machinery besides. According to Mr. Gooch's experiments upon a train
weighing 100 tons, the resistance of the engine and tender at 13.1 miles
per hour was found by the indicator to be 12.38 lbs.; the resistance per
ton of the train, as ascertained by the dynamometer, was at the same speed
7.58 lbs., and the average resistance of locomotive and train was 9.04 lbs.
At 20.2 miles per hour these resistances respectively became 19.0, 8.19,
and 12.2 lbs. At 441 miles per hour the resistances became 34.0, 21.10, and
25.5 lbs., and at 57.4 miles an hour they became 35.5, 17.81, and 23.8 lbs.

499. _Q._--Is it not maintained that the resistance of the atmosphere to
the progress of railway trains increases as the square of the velocity?

_A._--The atmospheric resistance, no doubt, increases as the square of the
velocity, and the power, therefore, necessary to overcome it will increase
as the cube of the velocity, since in doubling the speed four times, the
power must be expended in overcoming the atmospheric resistance in half the
time. At low speeds, the resistance does not increase very rapidly; but at
high speeds, as the rapid increase in the atmospheric resistance causes the
main resistance to be that arising from the atmosphere, the total
resistance will vary nearly as the square of the velocity. Thus the
resistance of a train, including locomotive and tender, will, at 15 miles
an hour, be about 9.3 lbs. per ton; at 30 miles an hour it will be 13.2
lbs. per ton; and a