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
miles of level at a mean rate of 9.7 miles per hour. On both levels
there were 141/2 chain curves of good length, and the speed, from 9 to 12
miles an hour, at which the train entered the respective levels, was not
quite regularly maintained throughout the half hour expended in running
over them. But if even 7 lbs. per tun of the total weight be taken as
the resistance at these speeds, the tractive force will be 11,004 lbs.,
which is more than one fourth the adhesion weight of 40,050 lbs. On
the next day, the same engine drew 30 wagons weighing 4661/2 tuns, or,
including engine and tender, 514 tuns nearly, up a gradient of 1 in
1171/2, three miles long, at a mean speed of 101/4 miles an hour. The
resistance due to gravity was 9,814 lbs., and supposing the other
resistance to traction to amount to no more than 7 lbs. per tun, the
total resistance would be 13,412 lbs., corresponding to a mean effective
cylinder pressure of 117 lbs. per square inch, and to a co-efficient of
adhesion of almost exactly one third.
"It is needless to repeat instances of much the same kind, as occurring
during the experiment referred to. The author is bound to say that they
were, no doubt, influenced by the favorable circumstances of weather,
and something is to be allowed also for the great length of train drawn,
very long trains having a less tractive resistance per tun on a level
than short ones, and something, possibly more than is commonly supposed,
may have been due to the use of oil-tight axle boxes, the saponaceous
compound known as 'railway grease' being nowhere in use on railways in
the States. It could not possibly be used, except in a congealed form,
in the severe American winters; and Messrs. Guebhard and Dieudonne's
experiments (_vide_ "De la resistance des trains et de la puissance des
machines." 8vo. Paris, 1868, p. 36) made in 1867, on the Eastern Railway
of France, showed a very considerable diminution in the resistance of
oil-boxed rolling stock as compared with that fitted with grease boxes.
But, weighed upon the other hand, are the facts, first, that the line
was of 6-feet gage, and, _pro tanto_, so much the worse for traction;
secondly, that the wheels were comparatively small, and the inside
journals of comparatively large diameter, the ratio of the former to the
latter being as 73/4 to 1, instead of 12 to 1 as on English lines. It is
difficult to believe that the length and steadiness of the double bogie
goods wagons, scarcely liable as they are to lateral vibrations, had not
something to do with the result, which is in some respects unique in the
history of railway traction. The result, although not absolutely showing