416 



THE POPULAR SCIENCE MONTHLY. 



conductors, and also to carry the conductor 

 in a conduit laid between the rails, connec- 

 tion being made between this conductor and 

 the moving car by a contact arm carried by 

 the car. The numerous difficulties appar- 

 ently inherent in all forms of surface or un- 

 derground conductors have led to their total 

 abandonment in this country in favor of the 

 overhead conductor familiarly known as the 

 trolley system. In this system the conductor 

 carrying the current to supply the moving 

 cars is strung on poles eighteen or twenty feet 

 from the ground, and connection is made be- 

 tween it and the moving car by means of a 

 long arm affixed to the roof of the car, and 

 carrying at its upper end a contaot, generally 

 in the form of a grooved disk. This arm is 

 held against the conductor by springs and is 

 controllable from the car by a rope connection 

 so that it can be pulled down out of connec- 

 tion with the conductor or readily replaced 

 when jolted out of position by the motion 

 of the car. Although this system has en- 

 countered much hostility on account of its 

 supposed danger, it has steadily made its 

 way on account of its capacity to adapt itself 

 to all manner and conditions of service, and 

 handle the varying traffic of a street railway 

 expeditiously, economically, and reliably. 

 Inventors are still busy working upon other 

 methods of applying the current, among which 

 probably the most promising is the storage 

 battery. Despite the fact that this method 

 is now in practical service upon two lines in 

 this country, it can not be said to have passed 

 the experimental stage, but it is very gen- 

 erally recognized that this would constitute 

 a final method of electric traction if it can 

 be worked out so as to have the reliability 

 and economy of the trolley system. 



This brief epitome of the work in electric 

 traction is set forth in detail by the authors 

 of the present volume. As they state, their 

 work is the first systematic presentation of 

 the subject, and it is therefore a welcome 

 addition to the current literature of the ap- 

 plications of electricity, the more so that it is 

 an extremely well executed one. One of the 

 editors is the editor of the Electrical World, 

 and has, therefore, been in a position to keep 

 himself informed on the history of the sub- 

 ject and to realize what the practical difficul- 

 ties have been in the development of the art. 

 The authors begin their exposition with a 



brief consideration of the general electrical 

 principles involved in the dynamo and elec- 

 tric motor, and then pass to a consideration 

 of prime movers, in which they devote con- 

 siderable space to the theory of the steam 

 engine as well as to a description of the best 

 types of engine to perform the work required 

 in electric traction. They also consider the 

 theory and best forms of water-wheels avail- 

 able. The forms of motors suitable, and the 

 method of mounting them upon the car so 

 as to apply the motion of the armature to the 

 driving of the wheels, are given an amount of 

 space commensurate with their importance, as 

 it is here that the largest amount of detail 

 labor has been necessary in working out the 

 practical problems of the system. A chapter 

 is given to the line, the track, and the power 

 stations, which deal with the practical con- 

 siderations to be taken into account in this 

 part of the equipment. In the chapter on 

 the efficiency of electric traction there is a 

 very excellent discussion of the subject, 

 ranging from the efficiency of the engine to 

 that of the complete system. A chapter is 

 given to storage-battery traction, in which 

 the authors describe the best forms of bat- 

 tery which have been devised, and point out 

 clearly the difficulties encountered with this 

 form of apparatus, and the large amount of 

 work that yet remains to be done before the 

 storage battery can take its place in econom- 

 ic competition with the trolley. In a chap- 

 ter on high-speed service an account is given 

 of the experiments conducted by Mr. Crosby 

 at Laurel, Md., with an electric car driven at a 

 speed of over a hundred miles an hour. The 

 authors believe that it is quite practicable to 

 establish an electric railway service in which 

 speeds of one hundred and fifty miles an 

 hour may be maintained, and give calcula- 

 tions of the power required and designs of 

 the electric apparatus and cars. The authors 

 conclude their volume with a chapter on 

 historical notes in which they detail the 

 early experiments in electric traction in 

 which the broad principles were worked out, 

 at a time when the electric battery was the 

 only source of current. Owing to a lack of 

 any economical source of electricity, these 

 early attempts resulted in nothing practical 

 in the way of the establishment of actual 

 roads, but they served the purpose of laying 

 the subject open to future workers and pre- 



