42 POWER DISTRIBUTION FOR KELECTRIC RAILROADS. 
just investigated, the resulting corrosion would amount to 
half a ton per year. 'This destruction would be done in the 
surfaces of exit from the pipe and if the conditions were 
such as to limit these surfaces to a comparatively small 
area the local damage would be very serious. 
Tilectrolytic corrosion of underground conductors by 
stray currents was first noticed in the case of lead covered 
telephone cables in Boston by I. H. Farnham, to whose 
researches much of our knowledge of the subject is due. 
Tead is attacked at the rate of about seventy-five 
pounds per ampere per year, so that the result is extremely 
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LEAD CABLE 
  
  
  
  
  
  
F16:- 20, 
marked. - Fig. 30 gives a diagrammatic view of the circuit 
through such a cable. Part of the current used on the 
railway circuit passes from the rails to the cable and thence 
along it to the neighborhood of the motors, where it passes 
back to the track and the moving cars. The mischief is 
done at this point and not while the current is flowing in 
the cable. ‘The effect produced is a severe corrosion of the 
lead covering of the cable taking place irregularly upon 
the surface and forming pits, which may penetrate the 
sheath and destroy the insulation of the cable. 
Investigation showed the state of things on the Boston 
system to be very interesting. At the time, the positive 
poles of the dynamos in the power station were connected 
with the rails so that the current passed into them and