ELECTRIC TRUNK-LINE OPERATION—SPRAGUE. 139 
not only a temporary cessation of drawing power by the locomotive, 
but there may actually be a return of energy to the line while slowing 
down. While of course this slowing down affects all trains on a sys- 
tem, it is quite conceivable that when there are a number of trains in 
operation a mean result may easily be attained which will, in the 
matter of load fluctuation, compare favorably with that of any other 
system. Multiple-unit grouping and operation is ordinarily imprac- 
ticable because of the small slip. In spite of the splendid work done 
by the Ganz Company, and the strong support of many Italian engi- 
neers, I feel that, all thmgs considered, neither the motor character- 
istics nor the limitations of overhead construction are acceptable for 
such service and conditions as exist on our trunk-line roads. 
On the other hand, considered by itself, the direct-current motor, 
with its high average weight efficiency, simplicity of construction, 
facility of control, automatic response in torque and speed to varying 
grades and curvatures, and great sustained capacity for enormous 
torque at low speed, besides the advantages of speed-ranges obtained 
by motor-grouping, and the use of a single conductor and track 
return, offers a most effective machine to meet the conditions of 
much of our railway service. Through it, as with the polyphase 
machine, the “ruling grade,” often of limited length, is eliminated, 
for the motor can always respond to these temporary demands up to 
the limit of track adhesion. 
Direct-current motor improvements.—During the last two years 
important developments have taken place in direct-current motor 
construction which materially change any preconceived conclusions 
as to its limitations. 
The first is the introduction of the commutating pole, which has 
practically eliminated commutator troubles, such as sparking, undue 
heating, and flashing over, so that even a four-pole machine, within 
a wide range of potential and load, runs absolutely black at the 
brushes. That this improvement has reached a high degree of com- 
mercial standing, despite very recent‘technical criticism and opposi- 
tion, is evidenced by the fact that orders for nearly a thousand such 
railway motors have been placed within the last two months. 
This improvement makes possible the shunted-field addition to the 
series-parallel control of speed, the construction of motors for opera- 
tion at much higher potentials, and the operation of two motors in 
series at double potential. 
An especially important development is that illustrated by the 
gearless locomotives built for the New York Central Railroad 
(pl. 1), in which the hitherto invariable practice of maintaining a 
fixity of relation between the armature, or rotating part, and the 
field magnet, or fixed part, has been abandoned; the armatures are 
