Feb. 27, 1855.] 



♦ KNOWLEDGE ♦ 



169 



Other wires, however, are connected at E F to the wires join- 

 ing the dynamo to the accumulators, and these other wires are 

 connected to the lamps in the various parts of the train. 

 It follows that, were there no electrical energy stored in the 

 accumulators, the current from the dynamo would divide 

 between them and the lamps. The accumulators arc never 

 wholly discharged, however; but, even were they so, sutlicient 

 charge would soon accumulate to prevent this division, for 

 it must be remembered that electricity, in chai-ging accumu- 

 lators, sets up a " counter electro-motive force," and if this 

 force is equal to that of the generator no electricity will flow 



S.WITCH 



into it, although a very small difference is sufficient to 

 maintain a current. Moreover, when the lamps and accu- 

 mulators are all in circuit, but little electricity will flow 

 into the latter, because the "difference of potential " be- 

 tween the dynamo and lamps is equal to that between the 

 brushes of the dynamo itself, while the " difference of 

 potential " between the dynamo and accumulators is only 

 a fraction of that amount ; and, as the greater proportion 

 of electricity flows between points of greater difference of 

 potential, nearly the whole current produced will be ab- 

 sorbed by the lamps. 



A switch is provided in the lamp circuit, so that the 

 guard may be able to disconnect it when the light is not 

 required. The current will then be utilised by the accumu- 

 lators. In the diagram, K L is the handle of the switch 

 hinged at K. When L is over A, the lamps are discon- 

 nected, but when it is over M, they are in circuit. 



One great feature of the Stroudley-Houghton system is 

 the automatic controlling apparatus. This originally took 

 the form of a governor, which was fitted in November, 

 1883; but in August, 1884, the work in the local train 

 was transferred to a mercury pump. This consisted of two 

 vertical tubes, the lower ends of which opened into a 

 cylinder. In this a coarse-threaded screw was made to 

 revolve by being connected to a small pulley-wheel, over 

 which passed a strap, which also passed round the spindle 

 of the dynamo. When the train was in motion the pulley- 

 wheel revolved, and with it the screw in the cylinder. The 

 cylinder and lower portions of the tubes being filled with 

 mercury, the revolution of the screw caused the mercury, 

 to fall in one tube and rise in the other. At a certain 

 height in each tube, above the normal level of the mercury, 

 was an adjustable contact point, and the mercury, on reach- 

 ing one or the other, completed tha dynamo's exciting 

 circuit. When the train travelled in one direction, the 

 pulley-wheel travelling with it would bring about the rise 

 of the mercury in one tube ; when it travelled in the 

 opposite direction the mercury would rise in the other tube. 

 The " shunt " circuit thus closed, in turn joined up the 

 main circuit automatically. 



There was another and most important function per" 

 taining to the mercury pump. The electromotive force 

 produced in the coils of a dynamo varies with the speed at 

 which the armature rotates. Accordingly, when running 

 slowly (or not running at all), the accumulators would have 

 a higher electromotive force than the dynamo, and if the 

 circuit between them were complete, the former would dis- 

 charge themselves through the coils of the machine. The 

 mercury pump, however, prevents this. The gearing 

 which drives the screw is so arranged that the mercury ia 

 made to rise in one of the tubes only when a speed of 

 twelve miles an hour is attained. At that speed the 

 dynamo runs fa^^t enough to produce the necessary electro- 

 motive force. 



The dynamo originally used was one of Messrs. Siemens' 

 machines (type D i). After some months, this was super- 

 seded by a" Brush machine, provided with a Schuckert 

 armature ; but any dynamo having the necessary electro- 

 motive force can be emi>loycd, and it is now proposed to 

 use dynamos which are free from the chief disadvantage of 

 a Brush machine — viz., that it will not respond to demands 

 for an increase of current in emergencies. The current 

 produced is one of .")G amperes, with an electromotive force 

 of 45 volts. A double set of " brushes " is provided, in 

 consequence of the frequent change in the direction in 

 which the armature rotates, and they are so fitted as to 

 work automatically. 



The thirty-two accumulators originally fitted were of 

 the first type of Faure cell, which did not answer so well 

 as was hoped, but those now employed give every satisfac- 

 tion, test well, and have been in daily use in the Pullman 

 Limited Express since December, 1882, showing a result in 

 every way satisfactory. There is this to be said, that the 

 vibration of the train may be calculated to do them more 

 good than harm. 



There are in the express train 5G, and in the local 

 train .39 Woodhouse and Eawson incandescent lamps, each 

 taking about ll-"i amprres, with an electromotive force of 

 40 volts. Other lamps have been tried, but Mr. Houghton's 

 experience is that their carbon filaments are too fragile to 

 withstand the vibration of the train, while the lamps now 

 in use have answered every requirement for the past eleven 

 months. 



A train fitted up on the Stroudley-Houghton system has 

 lately started running on the South-Eastern Railway, 

 between London and Maid.stone. 



The weight of the accumulators is about 22 cwt., and of 

 the dynamo 8 cwt., making in all 30 cwt. 



The local train, which offers certainly the severest test, 

 has been running continuously for fourteen months, making 

 about 3,200 trips, and running about 40,000 miles, giving 

 during that time every satisfaction. The trains have been 

 equipped by the Railway Electrical Contractors (Limited), 

 4, Great Winchester- street, E.C., and the result speaks well 

 for the managing-director, Mr. T. M. Collet. 



With reference to the relative cost of the system, com- 

 plete details cannot be given. The cost of the oil previously 

 consumed and wasted is saved, and this is a considerable 

 item. There is no cost for lamp cleaners, as the lamps 

 require no cleaning. The energy absorbed by the lamps is 

 but three electrical horse-power ; and, making the widest 

 allowance for waste in the dynamo and bearings, the 

 additional consumption of coal in the engine is small. Aa 

 a matter of fact, the driver is unable to detect any 

 difference in the consumption ; and many a time has it 

 happened that the driver has not been aware of the tact; 

 that he is lighting the train as well as drawing it, untd he 

 has arrived at the end of his journey. Practically, then, 

 the cost of the light is almost reducible to depreciation oi 



