164 POWER DISTRIBUTION FOR ELECTRIC RAILROADS. 
should have good inherent regulation so that lagging cur- 
rent will not reduce the voltage seriously and it is well to 
raise the initial voltage a little at the time of starting. 
Rotary converters when thrown into action may assume 
either polarity, but a few tentative touches of the switch 
with small current will secure an E. M. F. in the right di- 
rection. 
Both polyphase generators and rotary converters oper- 
ate well in parallel, behaving, in fact, much like continu- 
ous current generators, when they are once in adjustment. 
The process of throwing alternators in parallel is very 
simple if one remembers that the currents must be in 
phase as wellas of the same voltage at the moment of con- 
nection. The former condition is determined by phase 
lamps, the latter by the voltmeters. 
For general transmission for railway work the voltage 
should generally be from 5000 to 10,000, more often the 
latter. In favorable climates even higher pressures may 
be safely employed. ‘The best field for such power trans- 
mission is in ' cases of distribution over distances of fifteen 
miles and upwards under circumstances in which a specially 
favorable spot can be selected for the main generating 
station. 
When alternating motors can be conveniently ems- 
ployed on the cars, transmission from a central station at 
high voltage may become the rule instead of the exception, 
for with power delivered to the working conductors from 
static transformers requiring no attention there will be less 
excuse for long and heavy feeders. In the next chapter 
we will consider the application of alternating motors to 
service on cars and the relation of this practice to the 
development of long distance electric lines. The first 
steps have already been taken and the obstacles, particu- 
larly as regards long lines and high speeds, are neither 
very many nor very formidable, except for the inertia of 
older and well established methods.