A manual of the principles and practice of road-making: comprising the location, construction, and improvement of roads, (common, macadam, paved, plank, etc.) and rail-roads. By W. M. Gillespie ...

RESISTANCES. 269
For the CARS, the Frictional resistance is taken at 6 lbs. DOr
ton, as before.
The Atmospheric resistance is assumed as equal to the square
of the velocity, multiplied by the bulk of the train in cubic feet,
and that product by io-oo Each ton weight of the train is
supposed to correspond to 180 cubic feet. The atmospheric resistance obtained by this formula would equal that given by
Russell, in the case of a load of 553 tons. For a greater load,
this formula makes this resistance proportionally greater than
Russell's, and for a less load proportionally less.
The residual or oscillatory resistance is taken at only f- the
product of the velocity by the weight, instead of 1, as in the
former formula. Mr. Gooch considers this "oscillatory" resistance to be mainly the increased friction of the axle bearing
upon its collars, in consequence of the transverse vibrations at
high velocities, while Mr. Russell makes it include all the resistances remaining, after " friction" and " atmosphere" are deducted from the total amount.
Example 4. Let weight of train = 100 tons; velocity = 50
miles per hour; required the resistance to the motion of the
cars.
Friction = 100 X 6 6- - 600 lbs.
50 x 100
Oscillation X 00 -- 333
Atmosphere = 50 X 50 X 100 X 180 X T~o-no = 900
Total resistance of cars = 1833 lbs.
For the ENGINE and tender, the resistance is separated into
two parts. That caused by the friction of axles and machinery,
is (in pounds per ton of their weight) equal to 5, plus one half
the velocity in miles per hour. That due to atmosphere and load
equals Ti0-t4o of the square of the velocity multiplied by the
weight of the train. These resistances would of course be dif
ferent for each different engine.