ELECTRIC TRUNK-LINE OPERATION—SPRAGUE. 149 
The relation of potentials indicated in this table raises the question 
whether, in view of the disparity of current conducting capacity 
between an overhead system and the third rail, it is not also possible 
that a sufficiently high potential can be used on the latter if from a 
practical railroad standpoint the balance of advantages and objections 
should be enough in its favor to warrant its material extension. 
Some time ago I stated that in my opinion it was practicable to 
operate at double the ordinary potentials with a properly protected 
under-contact sheathed third rail. I am glad to be now able definitely 
to announce that it seems possible to construct and operate at these 
increased potentials with a degree of safety hitherto deemed doubtful. 
Fifteen-cycle operation.—The principal object sought, and cer- 
tainly a most desirable one in the use of higher potentials, whether 
direct current or alternating current, is not now so much reduced cost 
of working conductors on a trunk-line system—for practice has shown 
that this cost is not materially affected—but lessened feeder invest- 
ment, increase of substation distances, reduction of total substation 
capacity, and, in the single-phase yatem, the abolition of moving 
machinery in the substations. * * 
The degree of success of the alternating-current development will 
depend primarily on the development of capacity and all-round oper- 
ative features in single-phase locomotive and car equipments. The 
25-eycle motor (hitherto the only frequency actually installed for 
single-phase equipments), whether judged by individual comparison 
or specific equipments, as I have already illustrated, or the general 
testimony of electrical engineers of manufacturing companies, has 
proved inadequate when compared with its rival. To correct this 
defect it has been proposed to adopt 15 cycles as a standard of 
operation. 
This number of cycles has been under consideration for some time. 
Tt is successfully used by the Ganz Company in its polyphase installa- 
tions, it has been proposed in this country by the General Electric and 
Westinghouse companies for important work, and has lately been 
urged as a standard by a number of engineers. 
Motor and locomotive constructions—Motors are of the geared 
and gearless types, may be entirely separate units or partly integral 
with the truck frame, and may be wholly or partly spring-supported. 
Locomotive designs, influenced in part by the type of motor adopted, 
show a great variety of constructions, and may be very generally 
classed as rigid frame with all weight on the driving axles and without 
leading trucks, rigid frame with either single axles or bogie leading 
trucks, and bogie-truck locomotives, the bogies being pivoted under 
the cab, and sometimes lnked together. 
