SPECIAI, METHODS OF DISTRIBUTION. 97 
So far as apparatus is concerned the difficulty of some- 
what higher voltage does not appear to be very serious. 
With comparatively little modification the type of railway 
motor now common could be rendered suitable for pressures 
up to 750 volts certainly. ‘The principal changes would be 
in the armature winding and the commutator, which would 
have to be arranged with more segments to bring the volt- 
age per bar within safe limits. With the large and power- 
ful motors likely to be used on long interurban roads the 
task is by no means formidable, and should not involve any 
serious increase of cost. As regards the generators the 
case is similar. On very large units 1000 volts would 
probably involve difficulties.of some moment, since in de- 
signing machines for great outputs, 1000 k. w. and the 
like, it is somewhat troublesome to keep the volts per comi- 
mutator segment within reasonable limits even for 6oo 
volts. But under ordinary conditions a generator for 750 
to 1000 volts is entirely feasible, and for very large capaci- 
ties the direct coupled units, consisting of one engine and 
two dynamos, already largely used, are entirely available. 
Such a combination, shown in Fig. 58, may be very readily 
operated with the generators coupled in series, giving 1000 
volts across the mains, or if convenient, 500 volts on each 
side of a three-wite system. In some cases, where so much 
as 1000 volts is not desired, a boosting dynamo may be 
used with great advantage in connection with a 500 volt 
generator. 
At all events the question of supplying current ata 
pressure considerably in excess of 500 volts is very simply 
answered in any of the ways mentioned. 
One instinctively asks, too, why ordinary railway 
motors should not be operated regularly in series for work 
onn long lines, as they are very extensively employed now 
with series-parallel controllers. There is no good reason 
why this should not be done, save the danger of excessive 
and destructive voltage in case of accident to one motor. 
Of course, in ordinary series-parallel working, no acci- 
dent could throw on a single motor more than the 500 volts