50 POWER DISTRIBUTION FOR ELECTRIC RAILROADS. 
considerations of track stability and durability point to the 
use of the continuous rail which minimizes at the same time 
the electrical difficulties. 
It must be remembered that in long distance lines such 
as are found in interurban and similar work, the use of 
continuous rails is liable to cause trouble from insufficient 
resistance to expansion, as such roads generally lack the 
strong lateral support of the paving and are often exposed 
to more violent changes of temperature. On the other 
hand, in the case of such roads trouble from electrolytic 
action is usually relatively small or entirely absent, so that 
bonding is sufficient. Also, as will be explained later, in 
these roads for heavy service and rather high speed there 
may sometimes be good reason for using two trolleys, quite 
aside from all questions of ground return. 
Of course, when the alternating current motor is thor: 
oughly developed for railway service all danger of elec: 
trolysis will be past, whatever the character of the return 
circuit, but there will still exist every reason for making 
the rail return as perfect as possible from motives of economy 
alone. For when bad bonding can increase the total re- 
sistance of the track circuit ten or a dozen times, as has 
happened many times, the waste of energy due to the in- 
creased drop in the circuit becomes somewhat burdensome. 
For example, take a single track of ninety pound rail 
10,000 ft. long. With continuous rails the resistance per 
thousand feet would be 515 of an ohm and for the whole 
distance .033. With 200 amperes flowing, the drop would 
be 6.6 volts and the loss of energy more than one kilowatt. 
Now suppose each bond contact with its half of the bond 
wire to have a resistance of .0cor ohm. On each line of 
rail there would be 660 of these so that the total bond re- 
sistance of the track would be .33 ohm and the drop due 
to this bond resistance with a current of 200 amperes 
would be 66 volts. The corresponding loss of energy 
would be 13.2 k. w. more than enough to operate an 
extra car. At thecost of power generally found this waste 
would represent in the vicinity of 1000 per year net loss, a