THE RETURN CIRCUIT. 45 
easier path through the supplementary conductors. Hence 
electrolytic action was practically obviated so far as the 
cables were concerned. 
A measurement of the current thus collected from the 
telephone cables into a main ground wire from the station 
showed over 500 amperes capable, if flowing continuously, 
of eating away 37,500 lbs. of lead per year. And as this 
current did not include that which found its way to water 
and gas pipes, the real amount of current which left the 
rails and wandered home through underground conductors 
was considerably larger than the figure mentioned, prob- 
ably several times as great. ‘The distribution of this cur- 
rent is so irregular from place to place, as indicated on the 
map, that it would be very hard indeed to estimate the total 
proportion it bears to the whole current on the system. 
So far as data are available however they indicate that we 
would not be wide of the truth in saying that ten to twenty 
per cent of the current on the system may follow other 
paths than that through the rails and bonds. Even more 
than this may appear in occasional instances. So while the 
earth helps the return circuit directly but little, buried 
conductors may help very materially, perhaps to their own 
serious detriment. It should be remembered that the elec- 
trolytic action is not necessarily proportional to the differ- 
ences of potential such as are noted on the maps. The 
places most injured depend on local conductivity and some 
of the worst instances recorded have occurred where the 
measured potential difference was only one or two volts. 
Figs. 33 and 34 give a graphic idea of the kind of 
damage that is done to pipes by electrolysis from stray 
currents. Fig. 33 shows the effect of corrosion on an iron 
gas pipe, and Fig. 34 that on a lead water pipe. Both are 
from photographs of the ‘‘horrible examples.”’ As the 
action tends to become concentrated in spots, a pipe may be 
perforated in a rather short time. Iron water pipe has some- 
times been riddled in five to eight months. That this is 
easily possible may be readily seen, for suppose that con- 
ditions are such as to get in a certain spot a flow of half