244 POWER DISTRIBUTION FOR ELECTRIC RAILROADS. 
The normal resistances encountered by a moving 
rain may be roughly classified as friction, grades and air 
resistance. ‘The first mentioned, including all the ordinary 
tractive resistances, is usually ter or twelve pounds per 
ton of moving weight on good track. Anything below ten 
pounds is unusually good and few railway engineers would 
care to count on anything below eight pounds even under 
the most favorable circumstances, although lower results 
are probably now and then reached at high speeds. 
The atmospheric resistance used to be taken as varying 
with the square of the speed, but the work of Crosby and 
Pounds per sq. ft.of cross-section 
  
102220 30 40 50 €0 70 80 90 100° ‘110 - 120 - 130 
Miles per Hour Street Ry.Journal 
FIG. 127. 
recent experiments with fast running trains have made it 
certain that up to speeds of fully 125 miles per hour the 
air resistance increases very little faster than the speed. 
Moreover it can be greatly lessened by shaping the front of 
the locomotive into a plane or parabolic wedge. Fig. 127 
shows the results of Crosby’s experiments with whirling 
bodies in addition to several points approximately estab- 
lished by direct experiments on moving trains. The latter 
are somewhat uncertain owing to insufficient data concern- 
ing exposed surfaces, but the results given have been taken 
as large as the data permit, so that they are over rather 
than under the real resistances. 
From these data we can calculate the power required 
to drive a given train at, say, one hundred miles per hour. 
  
  
   
  
  
  
  
  
  
  
  
   
     
   
   
  
  
  
  
  
  
  
   
  
  
  
  
  
  
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