The curve in Fig. 1 would indicate that the energy derived from the two
sources just discussed is practically dissipated at 15 miles, though the
position of the points representing Items 16, 18, 19, 20, and 21 would
indicate that this takes place more frequently between 10 and 12 miles.
From this point onward the performance depends on the efficiency of the
steam production, which does not appear to be able to utilize more than
16% of the weight on the drivers. The diagrams presented by Mr. Dennis
in his paper on virtual grades, and by John A. Fulton, M. Am. Soc.
C. E., in his discussion of that paper, indicate that similar results
would be shown were they extended to include the distance named.
From this it would appear that a locomotive is capable of hauling a
larger train on grades less than 10 miles in length than on longer
grades, and that, even when unexpectedly stopped, it is capable of
starting again as soon as the steam pressure is sufficiently built up.
Conversely, it should be practicable to use a higher rate of ascent on
shorter grades on any given line without decreasing the load which can
be hauled over it. In other words, what is known as the "ruling grade"
is a function, strictly speaking, of the length as well as the rate of
grade.
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