SCIENCE 



FRIDAY, DECEMBER 14, i8£ 



ELECTRIC PROPULSION. 



Nov. 26 and Dec. 5 of the current year will be memorable dates 

 in the history of electric propulsion ; for on those days the lafgest 

 and most powerful electric railway-motor yet constructed gave 

 proof, on the Ninth Avenue line of the New York elevated railways, 

 of its capability to do all that the steam-locomotives there in use 

 are called upon to perform in their regular service. This motor was 

 the Daft motor ' Benjamin Franklin,' whose plan and side-elevation 

 illustrate this article. 



Electrical traction on a minor scale is no new thing : Siemens, 

 at Berlin and Port Rush, had accomplished it as early as 1881, and 

 Daft himself had achieved the first commercial success in this line 



The question will naturally suggest itself, ' What future has this 

 motor, and what are Us claims to preference over the system now 



in use on the New York elevated railways?" 



The answer is, radical economy, which lies in the recognized 

 wastefulness of small — especially locomotive — engines, and the 

 high efficiency of large stationary engines of improved type. Mul- 

 tiplication of power-generators implies loss in efficiency, and in- 

 creased cost of attendance. Derivation of power from one origin, 

 with ready capability of subdivision, is economy. The average 

 consumption of coal per horse-power, as between light rapid ex- 

 press and slow heavy freight-trains, is about nine pounds per hour 

 for steam-locomotives. A modern compound condensing engine 

 will yield a horse-power for two pounds per hour, or even less. 

 Admitting that the conversions from power to current, and vice 

 versa, consume one-third of this, it still remains that the locomo- 



DTOE FRANK 



— that is to say, the first electric railway ever built under a busi- 

 ness contract, completed and paid for in accordance therewith, and 

 •continued in operation without modification thenceforward — at 

 Baltimore in 1885 ; but nothing excepting the Pittsburgh motors of 

 35 horse-power, also of Daft's design, had passed the limit of 10 

 or 15 horse-power until the ' Franklin ' appeared on the scene. 



A general description of this motor follows ; and the cuts will 

 give a clear idea of its mechanical arrangement and details. The 

 total weight is ten tons, — very little over half the weight of the 

 •steam-locomotives in regular use, — and the wheel-base and length 

 •over all are respectively 56" and 14' 6". The total horse-power is 

 probably 150, although there has as yet been no opportunity of 

 making an ultimate test in this respect. 



The ' Franklin ' was designed to pull four cars and their seated 

 load — a total weight of 75 tons — over any gradient of the Ninth 

 Avenue Elevated Railway at the schedule speed of ordinary trains. 

 In the trials a train of eight empty cars — a load of 122 tons, 47 

 in e.\cess of that agreed upon — was taken up the maximum gra- 

 dient (nearly two per cent) at a speed of 7} miles per hour, and a 

 loaded four-car train exceeded the schedule speed by almost 3 miles 

 per hour. 



tive-engine needs more than three times as much coal as the sta- 

 tionary for every horse-power exerted upon the track. It is demon- 

 strable that the New York elevated railroads can be run at less 

 than half the present cost for motive power, including a charge for 

 interest on the cost of the new equipment, and ignoring the 

 proceeds derivable from the sale of the old. 



Other economical features of the system are, — 



1. Reduction of attendance. 



2. Conservation of permanent way from the diminution in weight 

 of motor permitted by its superior adhesion. This is always avail- 

 able where the rails constitute part of the circuit, and makes plain 

 why the ' Franklin," of half the weight of a steam-locomotive, can 

 haul as great a load. One of the most invaluable features of the 

 system is the high degree of adhesion between the motor-wheels 

 and the rails, which permits the employment of much lighter tractors 

 than would be practicable if steam-locomotives were used, to the 

 manifest advantage of the vehicles themselves and of the perma- 

 nent way. This adhesion is not magnetic, and probably results from 

 molecular change produced by the current in contiguous surfaces 

 of wheel and rail. It sometimes amounts to forty per cent of the 

 weight as opposed to twenty per cent usually obser^-able in steam- 



