with no aid from momentum. The average speed was 5 miles an hour, and
neither was the pressure of steam increased nor sand used except in
starting from the stops purposely made. The engine, even were its full
boiler pressure of 130 lbs. maintained as effective pressure upon the
pistons throughout the whole length of their stroke, could not have
exerted a tractive force greater than (17 x 17 x 130 lbs. x 2 ft.)/ 5
ft = 15,028 lbs.; nor is it at all probable that the effective cylinder
pressure could have approached this limit by from 10 lbs. to 15 lbs. per
square inch. Supposing, however, for the sake of a reductio ad absurdum,
that the full boiler pressure had been maintained upon the pistons for
the whole length of their strokes, the adhesion of the coupled driving
wheels, not deducting the internal resistances of the engine, would have
been 15028/40050 3/8 of the weight upon them. In any case there was
a resistance of 4,011 lbs. due to gravity, and if even 120 lbs. mean
effective cylinder pressure be assumed, corresponding to a total
tractive force of 13,872 lbs., the quotient representing the rolling and
other resistances, exclusive of gravity, would be but 6.27 lbs. per tun
of the entire train; a resistance including all the internal resistances
of the engine, the resistance of the curves, easy although they were,
and the loss in accelerating and retarding the train in starting and
stopping. This estimate of resistance would correspond, at the observed
speed of 5 miles an hour (upwards of 3/4 of an hour having been consumed
on the 4 miles), to 185 indicated H.P., which, with the driving wheels,
making but 28 revolutions per minute, would be the utmost that an engine
with but 1,038 square feet of heating surface could be expected to
exert. This was the highest result observed during the three weeks'
trial, but one or two others are worthy of mention. On the Delaware
division of the same line, the train, of 1,572 tuns' weight, was run
over 5 consecutive miles of absolutely level line, at a mean rate of
9.23 miles an hour, and during the same day, over 5 other consecutive