248 POWER DISTRIBUTION FOR ELECTRIC RAILROADS. 
for speeds like those considered, and ought to be insisted 
on even for present express speeds. With such a clear 
track and reduced speed, really running on momentum, in 
nearing termini, the braking effort required is by mno 
means out of reach. The momentum of a 140 ton train 
at 100 miles per hour is less than that of a 300 ton train 
at 60 miles per hour and about the same as that of a 300 
ton train at 50 miles per hour, and such trains are within 
the 1imits of present practice. To be sure, the number of 
wheels subject to braking would be much less in the elec- 
tric train, but on the other hand a powerful braking action 
. can be obtained by throwing the motors into action as 
dynamos through a resistance. 
It is not difficult to figure the braking action. Assum- 
ing, from one hundred miles per hour to rest, a coefficient 
of friction of o.1 between brake shoe and wheels, and a 
brake pressure of 5000 Ibs per wheel, we have for twenty 
wheels, eight on motor car and twelve on trail car, a net 
average retarding effort of 0.1 X 5000 X 20 = 10,000 1bs. 
The air resistance would average from our previous 
computation 500 lbs., and at least 2000 1lbs. could be 
counted on from the motors. The total retarding force 
would then be 10,000 4 500 —+ 2000 lbs. = 12,500 Ibs. 
The momentum of the train at one hundred miles per hour 
would be absorbed by this retardation in about 2500 yds. 
As a matter of fact 140 tons is needlessly heavy for a two- 
car train, and eventually high speed structures would be 
built much lighter than this. Itis, however, perfectly pos- 
sible to get the speed without departing from ordinary rail- 
way construction and the average man at present prefers 
this to being enclosed in the species of sheet steel projectile 
that has been thought necessary in many projects for high 
speed service. 
We may now take up the line question. The simplest 
method 1s to make the working conductor the transmission 
line, as previously suggested. For the working condi- 
tions, monophase transmission gives quite as great econ- 
omy as polyphase, for the immense conductivity of the 
     
   
   
  
     
  
  
  
  
   
   
  
   
  
   
T TR ST 
T 
SR 
g 
e 
S 
R 
R T R I 
TIR SIS,