THE RETURN CIRCUIT. 31 
20. 'The supplementary wire effectively prevents ‘‘ dead 
rails.”” In modern practice the bond wires are often as 
heavy as No. oooo, and are generally tinned to prevent 
corrosion. All joints in the wire are soldered and the rail 
contacts made as perfect as possible. It is perfectly clear 
that the supplementary wire is of little value as a con- 
  
  
  
  
  
  
  
  
  
  
  
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e i =y 1 
FIG. I8, 
FIG. IQ. 
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ductor compared with the rails, but it is of service in miti- 
gating the effects of bad joints. In a few casesthis supple- 
mentary wire is reinforced by a heavy copper conductor laid 
alongside the track and connected at intervals to the sup- 
plementary wire as shown in Fig. 21. If the joints made 
by the bonds and rail are very bad this extra copper may 
be of service, but good joints render it quite unnecessary. 
The value of the rails as conductors is so great that every 
effort should be made to utilize them to the fullest possible 
extent.