TBAKSACTIONS OF SECTION 0. 



743 



The salient points of a Series electrical tramway are a dvnamo, producing a 

 current of constant quantity — a closed metallic circuit of which trnvelling motors 

 ut all times form a part without ever beinf^ short-circuited, or having the current 

 supply cut off from them— the regulation of the power developed by the motor and 

 absorbed by it without interrupting the 

 continuity of the circuit. 



The ' Statter' dynamo, used at North- 

 fleet, varies the difference of potential at 

 its terminals from a few volts to upwards 

 of 400, maintaining the current constantly 

 at 50 amperes. This is achieved by au 

 ingeniously-designed electrical regulator, 

 which alters the position of the brushes 

 on t!ie commutator ; the pole-pieces of the 

 dynamo being so shaped as to reduce to a 

 negligablo quantity the sparking which 

 might be supposed to result from the 

 alteration of the lead of the brushes. 



A highly-insulated cable connected to 

 one terminal of the generator traverses 

 the whole length of the line, and is inter- 

 rupted at distances of 20 feet, the divided 

 ends being connected with the opposite 

 faces of a ' spring-jack,' which is at the 

 same time the automatic switch and con- 

 tact point. 



From the last ' spring-jack ' at the far 

 end of the line an uninterrupted cable 

 returns to the other terminal of the gene- 

 rator. 



The ' spring-jack ' consists of two gun- 

 metal 'cheeks' attached to glazed earth- 

 enware blocks by spiral springs, which 

 keep them in contact. 



The * arrow,' or current-collector, 

 which is the same length ns and is car- 

 ried by the car, is so constructed as to 

 pass between the faces of the ' spring- 

 jack' and conduct the current to the 

 motor without at any time short-circuit- 

 ing it or interrupting the main circuit. 



The motors at Nortlifleet run at 400 

 revolutions per minute, delivering a maxi- 

 mum of la horse-power on the brake, a 

 pinion on the motor-shaft gearing direct 

 with a spur-wheel on the car shaft, with 

 a ratio of 1 to 4i. 



A car is lighted electrically by low- 

 resistance ]5eriistein lamps, running off 

 the terminals of three accumulator cells 

 arranged directly in series with the main 

 circuit. 



The generator is driven by a com- 

 pound Bobey engine of 10 horse-power 

 (nominal), the steam being supplied from 

 a locomotive multitubular boiler. 



The conduit through which tlie 'arrow' or collector travels is arranged 

 directly under one of the running rails. This running rail ditl'ers from the ordi- 

 nary tramway rail, inasmuch as the tread and guard portions consist of two 



