September 2y, 1910J 



NATURE 



413 



In December, 1909, the electrified portion of the London, 

 Brighton, and South Coast Railway from Victoria, round 

 by Denmark Hill, to London Bridge was . opened for 

 traflic. This work marks an epoch in the history of 

 electric traction in England. For the first time the single- 

 phase system was applied to meet the exacting traffic con- 

 ditions of a London suburban service where the main 

 condition is that the trains should be accelerated rapidly. 

 The system has shown that it can meet all the conditions 

 of the service perfectly. Energy is purchased, and is dis- 

 tributed by overhead conductors direct to the trains at 

 6600 volts, single phase, at twenty-five alternations per 

 second, where it is used by the single-phase motors after 

 suitable transformation by apparatus carried under the 

 motor carriage. The results of this electrification will be 

 of unusual interest, because not only has the method 

 applied shown itself to be quite suitable for dealing with 

 a stopping trartic where quick acceleration is the domin- 

 ating condition, but it contains the germ of practicable 

 long-distance electrification. The near future may see the 

 e.\tension of the system to the line between London and 

 Brighton, giving a frequent non-stop service which would 

 bring Brighton in point of time nearer than the suburbs 

 on opposite sides ol London are to one another. 



Pinver Signalling. 

 During the last ten years a considerable number of trial 

 installations of power-signalling apparatus have been made 

 by the railway companies of this country. The electric 

 lines have generally adopted power signalling, and the 

 District Railway has installed a complete system on all 

 its lines and branches. 



The term " power signalling " is applied to any equip- 

 ment in which the actual movements of the points and 

 signals are done by power, the signalman's work being 

 thus reduced to the movement of small light control levers 

 or switches. Of the several systems tried and proposed, 

 three bulk largest in the equipments applied in this country, 

 namely, the all-electric, the low-pressure pneumatic, and 

 the electro-pneumatic systems. 



The " all-electric " system is represented by installations 

 of the McKenzie-Holland and Westinghouse system on the 

 Metropolitan and Great Western Railways, by installations 

 of the " Crewe " system on the London and North-Western 

 Railway, and by installations of Siemens Brothers on the 

 ('■rent Western Railway. The general feature of the all- 

 eleclric system is that the points are operated by motors 

 sunk in a pit by the side of the rails ; the signals are 

 pulled off electrically, and all the apparatus is controlled 

 electrically. 



The low-pressure pneumatic system is represented by 

 installations on the London and South-Western Railway 

 and the Great Central Railway. The points and signal 

 arms are moved by air compressed to about 20 lb. per 

 square inch, and led to cvlinders connected to the points 

 and to the signal arms. The control is also done by means 

 of compress-d air. small pipes leading from each air 

 cylinder to the cabin. 



The electro-pneumatic system has found most favour in 

 this country up to the present time. The equipment 

 installed includes such notable stations as the Central at 

 Newcastle with 404 levers, and the Glasgow Central with 

 374 levers, and the whole of the Metropolitan District 

 system of underground railways. In this system an air 

 cylinder is connected to each set of points and to each 

 signal-arm. .Air compressed at 65 lb. per square inch is 

 supplied to the cylinders from a main running alongside 

 the railway kept charged by small air-compressors placed 

 at convenient intervals. Each air cylinder is provided with 

 ri small three-way air-valve operated by an electromagnet. 

 The movement of each air-valve is controlled electricallv 

 from the cabin through the electromagnet associated with 

 it. The system grouped round any one signal-cabin may 

 be regarded as an .nginp fitted with a large number of 

 cylinders, each working intermittently by compressed air, 

 and where in each the valve-rod has been changed to an 

 electric cable, all the cables being led to a signal-cabin, 

 where the operation of the valves is done bv means of an 

 apparatus which is as easily played upon as a piano, with 

 this difference, however, that the notes are mechanically 

 interlocked, so that a signalman cannot play any tune he 

 pleases, but only a tune w^hich permits of safe traflic 

 NO. 2135, VOL. 84] 



movement. .Moreover, the instrument is so arranged that 

 the movement of the small lever determining the move- 

 ment of a signal-arm cannot be completed unless the 

 signal-arm actually responds to the intention of the signal- 

 man, thus detecting any fault in aie connections between. 

 the bo.x and the arm. 



The obvious advantage of power signalling is the large 

 reduction of physical labour required from the signalman. 

 His energy can be utilised in thinking about the traflSc 

 movements rather than in hauling all day at signal levers. 

 One man at a power frame can do the work of three at 

 the ordinary frame. The claims made for power signal- 

 ling, in addition to the obvious advantage of the reduction 

 of labour, are briefly that the volume of traffic which can 

 be dealt with is largely increased, that the area of ground 

 required for the installation is considerably less than with, 

 the ordinary system, with its rodding, bell-crank levers, 

 chains, and pulleys, and that where the conditions are such 

 that power signalling is justified the maintenance cost is 

 less than with a corresponding system of normal equip- 

 ment. 



Atttottiatic Signallitig. 



Several of the power-signalling installations are auto- 

 matic in the sense that between signal-cabins on stretches 

 of line where there are no junctions or cross-over roads, 

 requiring the movement of points, the movement of the 

 signal arm protecting a section is determined by the 

 passage of the train itself. The most important equip- 

 ment of this kind is that installed on the group ol rail- 

 ways forming the " Underground " system. This includes, 

 the District Railway with all its branches. On this line 

 the particular system installed is the electro-pneumatic, 

 modified to be automatic except at junctions. Signal- 

 cabins are placed only at junctions and at places where- 

 points require to be operated. The stretch of line to be- 

 automatically signalled is divided into sections, and the 

 entrance to each section is guarded by a signal-post-. Call- 

 ing two successive sections A and B, the train as it passes 

 from Section .-\ to Section B must automatically put the 

 signal at the entrance to B to danger, and at the same- 

 time must pull off the signal at the entrance to A. These 

 operations require the normal position of the signal-arm 

 to be " off " instead of at danger, as in the usual practice. 

 The position of the arm in this system conveys a direct 

 message to the driver. If " on " he knows that there is 

 a train in the section ; if " off " he knows that the section 

 is clear. Each signal-arm is operated by an air motor, as 

 brieflv described above, but the cables from the valves are 

 now led to relays at the beginning and end of the section 

 w-hich the signal protects. The contrivance by means of 

 n-hich the train acts as its own signalman is briefly as 

 follows. One rail of the running track is bonded, and is 

 connected to the positive pole of a battery or generator. 

 The opposite rail is divided into sections, each about 300 

 yards long, bonded, but insulated at each end from the 

 rails of the adjacent sections, and each section is con- 

 nected to a common negative main through a resistance.. 

 A relay is placed at the beginning and at the end of each 

 section, and is connected across from the positive to the 

 negative rail. Current flows and energises the relay, in 

 which condition the relay completes a circuit to the electro- 

 magnet operating the admission valve of the air cylinder 

 on the signal-post, air is admitted, and the signal-arm is 

 held off. This is the normal condition at each end of the 

 circuit. When a train enters a section it short-circuits the 

 lelavs through the wheels and axles, in consequence of 

 which the relays, de-energised, break the circuit to the 

 admission valve, which closes, and allows the air in the 

 cylinder to escape, and the signal-arm, moved by gravity 

 alone, assumes the " on " or danger position. At the 

 same time the short circuit is removed from the section 

 behind directly the train leaves it, the relaysare at once 

 energised, the admission valve to the air cylinder on the 

 protecting post of the section is opened, air enters, and 

 the signal is pulled down to the " off " position. 



The "speed at which traflic can be operated by this 

 svstem of power signalling is remarkable. At Earl's- 

 Court junction box forty trains an hour can be passed each 

 wav — that is, eightv per hour — handled by the one signal- 

 man in the box. As the train approaches the box, both 

 its approach to the section and its destination must be 



