44 POWER DISTRIBUTION FOR ELECTRIC RAILROADS. 
trouble as nearly as practicable in definite areas and then 
to check it in these areas. In the first place the dynamo 
connections were reversed so that the stray current would 
enter pipes and cables over the most of the system, but 
would leave them en route for the negative terminal of the 
dynamo only in the districts immediately surrounding the 
power houses. ‘Thus it would be certain that the damage 
would be limited to known areas which could be attacked 
locally with success, instead of being scattered where the 
trouble would be hard to locate and harder to remedy. 
  
  
  
     
     
CAMBRIDGE 
EAST BOSTON 
  
  
  
P16, 32 
Fig. 32 shows the result of thischange. The ‘‘ danger 
areas’’ shown here as before by shading on the map, are 
comparatively small, although within them the differences 
of potential were quite as great as before. Now the prob- 
lem was to lead the current back to the dynamo without 
compelling it to leave the cables, and corrode them at the 
points of exit. ‘To this end, large copper conductors were 
extended through the danger area and thoroughly con- 
nected at intervals to the telephone cables. The result 
was excellent, since the stray currents, instead of passing 
from the cables through the earth to the track, took the