TELPHERAGE 267 



merely mention it to let yon understand that in speaking of 

 three horse-power at the generator for one at the locomotive, I am 

 leaving a very ample margin. Quitting generalities, I will give 

 some details as to the electrical and other conditions necessary, 

 in two examples, for what may be considered as typical telpher 

 lines. 



-<t Line. Length, five miles. Length of circuit, out and 

 in. ten miles. Twenty-five trains running at once, spaced one- 

 fifth of a mile apart ; speed four miles per hour. Let each re- 

 quire 1 horse-power on the average ; let the motor take on the 

 average two amperes of electric current ; let the electromotive 

 force near the stationary engine be 840 volts ; the electromotive 

 force at the end of five miles will be about 746 volts. 1 The total 

 current entering the line will be 50 amperes at the near end of 

 the line. Fifty amperes and 840 volts represent 56'5 horse- 

 power ; of this, 6-5 horse-power will be wasted in heating the 

 line ; the remaining 50 horse-power will do work in the motors 

 equivalent to 25 horse-power. In order to give this current of 

 50 amperes with 840 volts, the stationary engine will require to 

 exert '^ x 56 '5 horse-power, or roughly, 70 indicated horse-power, 

 or somewhat less than three times the useful horse-power. Let 

 us now examine the economical results to be obtained from such 

 a line as this. Mr. Dowson, in an interesting comparison be- 

 tween the cost of horse-power obtained from coal and gas, reckoned 

 the cost per horse-power for a 100 horse-power engine, at the 

 rate of 31. 6s. 9d. per annum, to include wages, coal, oil, and 

 depreciation. Mr. Dowson would naturally be led to put the 

 cost of steam power obtained from coal rather high than low. I 

 will, however, adopt a much higher figure, and assume that the 

 power may cost as much as 01. 10s. per horse per annum ; this 

 gives 4ool. as the cost of the 70 horse-power required for my 

 telpher line. Let the twenty-five trains each convey a useful 

 load of 15 cwt. In a day of eight hours the line will have con- 

 veyed a traffic which we may express as 600 ton-miles i.e. it 

 will be equivalent to 600 tons conveyed one mile, or 60 tons on 

 each line conveyed from end to end daily. If we count 300 



1 It has been suggested that this fall of potential would be inconvenient. 

 For electric lighting, it would be too great ; but in telpherage it would simply 

 cause a decrease in the speed of the train at the far end, and as all trains 

 would be equally affected, none would overtake the other, and no inconvenience 

 whatever would arise. 



