38 POWER DISTRIBUTION FOR ELECTRIC RAILROADS. 
earth than Fig. 27. 'The rails are here supported at each 
tie by cast iron chairs, without an intermediate stringer, 
and the ties are set in concrete, while rail and chair are 
surrounded by coarse gravel on which the paving is laid. 
In no modern track is the rail in contact with better con- 
ductors than hard wood, gravel or stone. Consequently 
there is very little tendency for current to be shunted from 
rails to earth, unless the former are very badly bonded, 
  
    
         
      
    
  
  
   
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for the paths in derivation are bad and there is little differ- 
ence of potential between any two points of the track to 
impel branch currents of any kind. Of course, if one at- 
tempts to use the two rails as outgoing and return leads, 
the condition is wholly changed, for the full difference 
of potential then exists between two mneighboring rails 
and there must be a very large amount of leakage. In 
fact, if there is any considerable difference of potential be- 
tween the rails or between them and any other conductor, 
there will be a perceptible flow of current, even through 
as bad a conductor as damp gravel, if the path be not 
too long.