36 POWER DISTRIBUTION FOR ELECTRIC RAILROADS. 
about four miles in length. ‘I'he ground plates themselves 
were of ample area, in one experiment several hundred 
square feet, and gave every opportunity for good contact 
with the water. The applied voltage in each set of ex- 
periments was 500 to 550. The resulting currents were 
insignificant and the resistance of the earth return proved 
in one case to be about 85 ohms, in the other but a few 
ohms less. 
In another more recent experiment the terminal sta- 
tions were about 3000 ft. apart. An attempt had been made 
to use an earth return for a motor circuit, with the usual 
result, and the failure led to investigation. The experi- 
ment was arranged as in Fig. 26. At A and B were care- 
fully arranged ground plates in duplicate. One of each 
pair was sunk in a well, the other imbedded in a mass of 
iron filings in damp earth. At1, 2, 3, 4, 5, stations 500 
ft. apart, grounds were made by driving large iron bars 
deep into the earth. The voltages employed were vari- 
ous, from 60 to 150 volts direct current, and alternating 
current from a small induction coil. The results were 
nearly coincident in all the sets of experiments and showed 
the following curious state of affairs: 
Stations. Res, ohms. 
A B 92.4  Ground plates alone. 
A B 121.0 Well plates alone. 
e Aol 66.8 Both well and ground plates. 
Pl L 201.6 
A2 374.0 
? A s 92. 
AT 506.3 
A a5 180.0 
T'he resistance is evidently not a function of the distance 
nor of anything else that is at all obvious. The only 
feature that is what might be expected, is the tolerably 
regular effect of putting both sets of earth plates in parallel 
as exhibited in the first three lines of the table. The re- 
sistances at the intermediate stations show how hopeless 
it is to predicate anything of earth resistance except that