THE RETURN CIRCUIT. 37 
it is too high to be of any practical use save for trivial 
currents such as are employed in telegraphy. 
These experiments are in keeping with many others, 
all tending to show that unless on a very small scale the 
earth is nearly useless as an electrical conductor. Asa 
conductor in parallel with a pair of heavy and well bond- 
ed rails, the earth is hardly to be seriously considered 
at all. 
Imagine the stations A and B, Fig. 26, to be con- 
nected by a track consisting of a pair of sixty pound rails 
thoroughly connected and put in parallel with the circuit 
via the earth connections. At best this has a resistance 
of 66.8 ohms while that of the track should be at worst 
only a few tenths of an ohm. Following the ordinary law 
of derived circuits, it is clear that the current returning via 
. 1 2 3 4 5 e 
FIG. 26. 
the earth is only a minute fraction of one per cent of the 
whole. If the track could be continuously in good con- 
tact with the earth throughout its length somewhat more 
current might be coaxed into the earth return by taking ad- 
vantage of all the fairly conducting streaks and strata. But 
in practice, track is so laid that it is not in good electrical 
contact with the earth asa whole. Fig. 27 shows in sec- 
tion a type of track construction which has been very 
widely used. 'The rail is laid upon a longitudinal stringer 
timber to which it is spiked firmly. ‘Thestringer is secured 
to the cross ties by angle irons. ‘The ties are well tamped 
with clean sharp gravel which is packed around them and 
the stringer, and forms a foundation for paving of block 
granite set closely in upon the rail. Here the material in 
contact with the rail and surrounding it for some space 
is very badly conducting except when the track is 
flooded. 
Fig. 28 shows another track construction, which would 
appear to give even worse conduction between rail and