40 



NATURE 



[May 9 1889 



one that was opened for public traffic at Northfleet, 

 on April 29. 



The track itself does not at first sight appear to differ 

 from an ordinary horse tramway track, there being no 

 overhead wires as in the American electric tramways, 

 nor auxiliary raised insulated rail, as at Portrush, nor 

 central trough, as at Blackpool. A closer inspection. 



however, shows that one of the rails at Northfleet, instead 

 of being simply grooved, is a double rail with a cavity or 

 slot between the two portions. Fig. i shows the general 

 cross-section of the line, the upper portion only of which is 

 of course visible to the passer-by. In the cavity "the arrow," 

 as it is called, glides, being drawn along by the moving 

 car, the function of the arrow being to open the electrical 



FjG. I. 



conductor at successive points, and insert the electric 

 motor carried by the moving car in the electrical circuit. 

 This arrow is made of flexible leather with a kind of 

 steel spear-head at each end ; it is coated with two 

 flexible conducting strips, i, 2 (Fig. 2), insulated from 

 one another, and permanently connected respectively 

 with the two terminals of the motor. As this arrow 



glides along, it passes, as seen in Fig. 3, between the^two 

 portions of each spring-jack, the spring-jack being shown 

 in detail in Fig. 4. The arrow keeps open two spring- 

 jacks at any one time, the portion of the cable joining 

 them being either cut out of circuit or short-circuited, its 

 place in the electric circuit being temporarily occupied by 

 the motor on the car. This result is attained by the con- 



FiG. 2. — The Arrov. 



ducting-Strips i, 2 (Fig. 2) on the arrow, being each 

 wrapped round one end, and by an insulated space, 3, 3, 

 being left on each side, slightly longer than the surface 

 of contact B of the spring-jack. When the sceptical 

 Englishman, who, in the past, could not realize that rail- 

 ways could ever succeed if the carriages were not shaped 

 and painted like mail-coaches, reads a description of the 



Northfleet series tramway, he at once jumps to the con- 

 clusion that stones must necessarily get wedged in the 

 slot ; that the cavity will get filled up with mud ; that 

 the arrow must stick ; and that the method is impossible 

 in practice, though very pretty in theory. When he is 

 told that a series electric tramway has been running 

 successfully for some time in Denver, Colorado, and that 



^ 



^ I T^ I T j^ ^tppp^^ -^ >| 



DYNAMO 



MOTOR 



1 UNDERGROUND CABLE! 



Fig. 3.— Diagrammatical Illustration of Series Line. 



another ser/es line, twelve miles long, with forty cars on ! 

 it, is completed, or on the verge of completion, in Colum- | 

 bus, Ohio, he merely shrugs his shoulders and implies \ 

 that such crude ideas may do for America, but that in 1 

 this country we want time-honoured well-tried methods, I 

 and not new-fangled notions. The Northfleet cars, how- i 

 *^vp.r. seem to have a marked disregard for conse rvative I 



prejudices, since the arrow, with an ease and lofty contempt 

 that makes one respect the silent power of the electric 

 current, simply whisks out of its way any stone that has 

 been intentionally jammed into the slot as tightly as any 

 mischievous London urchin can fix it. 



The spring-jack (Fig. 4) consists of a pair of glazed 

 earthenware blocks, 14 X 3 X 4 inches. To each block 



