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.

In any discussions of the practicability of using a higher rate on the
short grades, which the writer has seen, the most valid objection has
appeared to be the danger of stalling and consequent delay. As far as
momentum is relied on, this objection is valid. Within the limits of the
load which can be handled by the steam, it has small value, as it is
only a question of waiting a few minutes until the pressure can be built
up to the point at which the load can be handled. As this need only be
an occasional occurrence, it is not to be balanced against any material
saving in cost of construction.

The writer does not know of any experiments which will throw much light
on the value of heat storage as separated from momentum, though the
following discussion may prove suggestive:

A train moving at a rate of 60 ft. per sec., and reaching the foot of a
grade, will have acquired a "velocity head" of 56.7 ft., equivalent to
stored energy of 56.7 x 2,000 = 113,400 ft-lb. per ton. On a 0.002
grade (as in Item 15 of Table 1) the resistance would be, gravity
4 lb. + train 4.7 lb. = 8.7 lb., against which the energy above given
would carry the train through 113,400 / 8.7 = 13,034 ft., say, 2.5
miles, leaving 5 miles to be provided for by the steam production.
Examining the items in the table having grades in excess of 10 miles, it
will be noted that 16% is about all the weight on drivers which can be
utilized by the current supply of steam. In Item 15 the energy derived
from all sources is equivalent to 24.3%; hence the stored heat may be
considered as responsible for an equivalent of 24.3% - 16% = 8.3% for a
distance of 5 miles.

TABLE 1.

===========================================================================
Item No.
|Length of grade, in miles.
| |Rate of grade.
| | |Maximum curvature.
| | | |Compensation.
| | | | |Gross weight of load, in tons.
| | | | | |Weight of tender, in tons.
| | | | | | |Weight of locomotive, in tons.
| | | | | | | |Weight on drivers, in tons.
| | | | | | | | |Percentage of weight on
| | | | | | | | |drivers utilized in draf