CHAPTER XIV.

LOCOMOTIVES AND ROLLING-STOCK.

CONTENTS.-Electricity as a motive power-Various systems of applying itTelpherage--Electrical traction on steep gradients-Electrical traction in England-City and South London-Central London-Liverpool Overhead-Motor cars or separate locomotives-Claret-Vuilleumier system-Overhead wire and trolley for light railways-Electrical traction in the States- Belt line tunnelOverhead and trolley system practically universal in the States-Nantasket Beach line-Heilmann electric locomotive in France-Steam generally best for goods traffic-Other methods of traction-Quantity of rolling-stock requiredDimensions of rolling-stock--Four or six-wheels coupled tank engines-Adhesion, tractive and hauling power of locomotives-Goods stock-Passenger stock-Belgian light railways stock-Decauville stock-Eastern Bengal State railway stock on three gauges-Barsi light railway stock.

Electrical Traction. Our choice of motive power on light railways lies practically between steam and electricity. The claims of the latter deserve particular consideration when the service to be provided is a regular and frequent one of comparatively light trains carrying passengers. For an almost continuous traffic of this sort, with loads which vary little from the average, electricity is eminently suitable, demanding no very great expenditure on generating plant and mains to begin with, and offering a fair prospeet of economy in working; while every addition to such a service would, if steam were adopted, call for an increased number of locomotives, and an increased expenditure on fuel and other running requirements. In tunnels the difficulties of ventilation would be largely minimised by electrical traction; and in the streets of towns-where the noise, smoke, dust and smell, due to the use of steam, are especially objectionableelectricity has obvious advantages. Although, therefore, steam locomotives may long continue to be regarded as the most economical and practical movers of irregular and intermittent traffic of the usual kind in the open country, they have less opportunity of exhibiting their speed and power in the neighbourhood of ordinary street or road traffic; and more and more shall we see them displaced by electric motors on our underground railways and the lines which serve our cities and suburbs.

The dynamo-electric machine was known, first of all, as a means of producing electrical energy by an expenditure of mechanical work.

When it was also recognised that its function could be reversed, and that it could act as a motor to perform mechanical work when supplied with energy in an electrical form, its applicability to purposes of railway traction began to be determined. Electrical traction* may

be applied in several forms:

:

I. Storage batteries may be employed to drive the motor, the batteries and motors being carried—

(a) in the car, which is to be preferred as more economical, if space is available, or—

(b) on a separate locomotive.

II. Various conductor systems are more commonly adopted

(a) Ordinary rails may be used as conductors, but are unsuitable to urban lines where the rails lie flush with the surface of the road;

(b) Nor is the use of a third insulated rail-laid in the centre of the track-above ground suitable in such cases.

(c) Overhead conductors—either the wire and trolley arrangement, or slotted tubes and contact carriages in the form of pistons sliding in the tubes and, for light railway purposes, the wire and trolley system is pre-eminently suitable and economical.

(d) Underground conductors in a slotted channel or conduit are less suitable to street or road work, and are much more expensive.

(e) Messrs Ayrton and Perry devised a system, by which the line was divided into short sections, each having an exposed conductor— it might be one of the rails-placed, as the train passed over it, in temporary contact with a well-insulated conductor in a closed underground channel by means of automatic electro-magnetic switches. Leakage was thus reduced to a minimum.

Another method of electrical locomotion, known as "telpherage," was proposed by the late Prof. Fleeming Jenkin, and developed by him in conjunction with Messrs Ayrton and Perry. It was intended for the slow carriage of goods in localities where the traffic was not enough to pay an ordinary railway, and has been tried in Japan and some of our own colonies. The line itself is singular, consisting of a steel rod or cable, suspended from brackets fixed to posts erected about 70 ft. apart. This rod or cable is not only a carrier of trains, but a conductor of the motive power-electricity. If the "telpher" line is made more rigid, the trains may be carried at higher speed. Generally, however, it is flexible, and the trains are run slowly, but, if the traffic requires it, they can be run in an almost continuous stream. The train consists of a series of buckets or skips, hung from a single wheel, or a pair of wheels, and they are spaced by wooden bars. The locomotive is formed by a small electric motor hanging below the line, and connected by spur and chain gearing with a pair of driving wheels. In general, the line is electrically divided into sections of nearly the same length as that of a train. The train is furnished with a continuous conductor from end to end, through

which it makes electric contact between the section in front and that behind, and the motor is included in the circuit of this conductor.

The ease and rapidity with which electrically-moved cars can be stopped or started even on steep inclines-a cruel strain on horses— render them singularly suitable for tramway purposes. Their speed can be checked or graduated to meet any requirement or emergency. Far steeper gradients can be faced on such lines than on other adhesion railways, owing to the reduced dead weight of the motive apparatus, and the gain in tractive power where motor-cars are used; so that in America* short gradients of 12 per cent. are not unknown, while gradients of 8 per cent. are common. The steep line from Florence to Fiesole, which may be known to the reader, is worked by motor-cars weighing 7.5 tons, with a tractive force of one-fifth of this weight, or 1.5 tons. The locomotives of the City and South London Electrical Railway (which the writer had the privilege of visiting shortly after its being opened), in hauling-including their own weight -as much as 30 tons up a gradient of 1 in 14 with sharp curves, develop tractive energy equal to a coefficient of adhesion of onefourth, such as must be expected, observed Dr Preller, † from a good electrical locomotive, as compared with a coefficient of adhesion of only one-sixth or one-seventh in the case of steam locomotives.

It is very remarkable that this application of electricity has hitherto in England been almost entirely confined to such special and important works as the City and South London Railway, the Liverpool Overhead Railway, the Waterloo and City Railway, and the deeplevel lines which are now being carried under the crowded thoroughfares of London.

On the City and South London † the generator station is at Stockwell. There are eight Lancashire boilers and four vertical compound engines, each driving a generating dynamo of the Edison-Hopkinson type. The switch board is so arranged that any of the four generators can be coupled to any of the four feeders either independently or in parallel. Two of the feeders are connected to the working conductors at Great Dover Street Station, 12,800 ft. distant. The other two are coupled in parallel to Stockwell, and one is continued to the Oval, where it is connected to working conductors, 14,330 ft. from the generator station. The cables consist of a stranded core of 61-14 B. W. G., insulated and sheathed with lead. They are carried along the tunnels on bracket supports. The working conductors consist of channel steel laid between the rails, and carried on glass insulators fixed to alternate sleepers. Each locomotive is provided with three collectors. The return circuit is through the uninsulated rails. The

* Min. Proc. Inst. C.E., vol. cxxv., "The Limiting Gradients on Adhesion Tramways," by F. Denizet, For. Abs.

+ Min. Proc. Inst. C. E., vol. cxii., "Hopkinson on Electrical Railways," 14th Feb. 1893.

armatures of the motors are built directly upon the axles of the locomotives, while the magnets are supported partly on the axle and partly on the frame. By thus adopting the principle of direct driving, the necessity of gear of any description is done away with, and the mechanism is, therefore, as simple as possible. There are two directacting motors on each locomotive, each motor capable of developing 50 h.p. at 25 miles an hour.

The locomotives for the Central London Underground Railway* are built by the General Electric Company at Schenectady, U.S.A., in accordance with the specification of the British Thomson-Houston Company. The tunnels have a bore 11 ft. 6 in. in diameter. The lines are carefully graded for starting and stopping with the assistance of a series of comparatively steep descents and ascents from and into stations. Trains of seven carriages will afford seating accommodation for 336 passengers, and weigh 105 tons loaded, exclusive of the locomotive. Of these carriages, 32 will be required in regular service. All trains are to be fitted throughout with the Westinghouse air-brake. The maximum speed is estimated at 30 miles an hour, and the average speed (including halts of twenty seconds at stations) at 14 miles an hour. The following details of the locomotive are given :—

On the Liverpool Overhead Railway motor carriages are used, and Mr Greathead admitted that, if there was head-room and the motors could be placed under the carriages, and if the trains were short, motor carriages were to be preferred, because the weight hauled was reduced and terminal London, however, +

* Street

avoided. On the City and South room for the motors under the

national Edition), March 1898.

carriages, the curves were too sharp to admit of longer carriages being built, and, it being a question of the multiplication of vehicles in any case, it was decided that separate locomotives should be provided.

The economy of the motor-car, as compared with haulage by a separate locomotive, may be illustrated by Mr W. Baxter's analysis* of the weights in two given cases. He takes a five-car train and gives the following figures:

In the latter case the weight of the motors is not more than 11.5 per cent. of the weight of the train, while the weight of the whole train is also reduced by 25 per cent., with a corresponding saving in driving power.

There is in England a very strong objection to the multiplication of overhead conductors in our large towns, and this is largely responsible for the small number of electric tramways hitherto constructed in this country. The use of accumulators, of the present types, has proved to be commercially a failure, owing to the high cost of maintenance; while underground conductors, on the culvert and slot system, are rarely adopted, on account of the heavy expense-amounting to as much as £1500 to £2000 per mile-of their construction. Nor is the underground conduit generally accepted as a satisfactory solution of the question of electric traction in our streets, because of the width of the slot; although at Buda-Pesth this is made as narrow as threequarters of an inch. A better solution, it has been suggested, is to be found in another example, that of an electric railway in Paris on the Claret - Vuilleumier system of conveyance by underground conductors, which was brought forward when the accumulator system had been proved to be a failure. The current for the motors is collected by brushes fixed underneath the cars and pressing on a rail flush with the surface of the ground, the track serving as a return. This rail is in sections, each a little shorter than a car, and each group of 18 sections is connected by rubber cables to an automatic apparatus called a 66 distributor," which is the feature of the system. The sections of each group are successively excited by the distributor as the car passes over them, those not covered by a car being insulated. A spare distributor is carried by each car, and can be substituted for a faulty one in a few minutes. To prevent horses from slipping, the conducting rail is made up of metallic blocks, eight feet apart,

* Min. Proc. Inst. C.E., vol. cxxvi., "Electric Transportation," by W. Baxter, jun. For. Abs., 1896.

+ Min. Proc. Inst. C.E., vol. cxxvi., "Electric Tramway in Paris," by Ch. Jacquin. For. Abs., 1896.