LOCOMOTIVE POWER - Locomotives may broadly be reduced to two classes, according to the situation of the working cylinders. In the first class these are within the framing, under the boiler, with the main driving axle cranked at two points to receive the power from the two cylinders ; in the second class they are outside the framing, and connected, not to the axle, which is straight, but to crank-pins fixed between the spokes of the wheels, in connexion with the nave. From these distinguishing features the two types of engines are known respectively as " inside cylinder locomotives" and "out-side cylinder locomotives." In the latter the general contour of the cylinders is usually visible at the fore-end of the machine. The tenders have six or four wheels, according to the ta.ste of the designer, and they are supplied with powerful brakes, worked by screws, with blocks of wood placed against each wheel. A water-tank forms the upper part of the tender, namely, the two sides and the back, usually in the form of a horse-shoe, holding from 1000 to 3000 gallons ; and in the hollow of the shoe the fuel is deposited, of which a full charge may weigh from 30 ewt. to 3i tons. The engine and the tender are sustained on springs placed over the axle-bearings. Again, there is the general classification of locomotives into passenger engines and goods and mineral engines. As the power of the engine is brought into action through the grip of the driving wheels upon the rails, it is necessaiy, for the exertion of maximum power in goods engines, to make two or more pairs of the wheels of one size, and transmit the driving force from the central pair of wheels to the front and back pairs by means of conpling-rods attached to crank-pins at the naves of the wheels. Such engines are called " six.coupled," and for them the most convenient combination is with inside cylinders. When the cylinders are outside it is usual to couple only the hind pair of wheels to the driving wheels, making a " four-coupled " engine, the leading or front wheels being of smaller diameter than the driving-wheels, and so leaving room for the convenient placement of the cylinders. The six-coupled engine can take the heaviest train on a. good straight railway, - that is, one free for the most part from curves ; but four-coupled engines work more economic-ally on lines with frequent curves, and may be made so as to take, in average practice, as great a load as six-coupled engines. Pass-enger locomotives have usually been constructed with a single pair of chiving-wheels, for free running at high speeds ; but as traffic became heavier four-coupled-wheel passenger engines came into vogue and express trains are•noNv for the most part worked with four-coupled engines. In recent years the forepart of engines has in many cases been placed on a four-wheeled truck connected by a central bolt or pivot to the frame of the engine, so that the fore-wheels can swino. to the curves of the line. On the Aletro-politan, Metropolitancbistriet, and North London Railways entirely, and on many large railway systems partially, where sharp curves are frequent, bogie-engines are employed, and with great advan-tage in facilitating traction. Another device for the same purpose is the use of radial axles, - that is, axles either at the forepart or the back of the engine, which by their axle-boxes slide laterally between circularly formed guides on entering and on leaving curved parts of the Is-ay, and so maintain a radial position at right angles to the line of rails.

American practice, many years since, arrived at two leading types of locomotive for passenger and for goods traffic. The passenger locomotive has eight wheels, of which four in front are framed in a bogie, and the four wheels behind are coupled drivers. This is the type to which English practice has been approximating. The tender is carried on eight wheels, disposed under two trucks or bogies, fore and aft. Goods locomotives are made with eight wheels and with ten wheels, of which, in each case, the leading pair of wheels are connected with a swing bolster and radius bar, to conform laterally and radially to curves.

As the speed increases a more than proportional increase in the engine-power is necessary to draw a given train. Thus, if an engine and tender, weighing together 40 tons and exerting a given tractive force, takes, say, forty loaded carriages, weighing 360 tons, at 20 miles per hour on a level, the loads which it could take if it exerted the same tractive power at higher speeds would be only as follows : - At 20 miles per hour, 40 carriages, weighing 360 tons. ' „ 40 „ „ 21 „ 77 144 „ _ _ .

Incline 1 in 600, 34 „ „ 340 „ „ 300, 27 „ „ 270 „ „ 150, 20 ,, „ 200 „ „ 100, 15 „ „ 150 „ )7 77 30, 5 ,, 45 „ „ 20, 8 „ „ 21 „ „ 10, nit „ „ nii „ This is the reason why the older railways were made nearly level at an enormous cost, - the elder Stephenson's policy being to incur a large expenditure in construction in order to avoid otherwise heavy inclines and heavy expenses. The ruling gradient of the Liverpool and Manchester Railway was fixed at 1 in 900, excepting, of course, the inevitable inclines at Rainhill summit, for working which special provision was made ; that of the next great line, the London and Birmingham, was fixed at 1 in 330 ; on the Great Western Railway, one of the earliest made lines, the ruling inclina-tion is 1 in 1320 for the greater part of the way. Locke, as already explained, initiated the system of cheaply constructed railways, as the facilities for increasing the power of locomotives became better understood ; he constructed lines with long steep gradients, some of them 1 in 70, 1 in 75, 1 in 80. The Great Northern Railway, of comparatively recent origin, was constructed on a ruling gradient of 1 in 200 ; and, in general, the more recently made lines have the steepest gradients. Steep railways are generally also lines of frequent curves, which is another cause of loss of locomotive power. Aloreover, the ruling speeds, as they may be called, have in the course of years increased. Thus in every way more powerful entgines are now needed than in the early days of railways.

The fundamental characteristics of English practice are fairly represented by a few types of locomotives. Take first an express passenger locomotive, which stands on a wheel base - the distance apart of the centres of the extreme axles - of 15 feet 4 inches. The cylinders are inside and are 16 inches in diameter, with a slide of 22 inches. The driving-wheels are 7 feet in diameter. The fire-grate has an area of 18 square feet, and the heating surface of the fire-box and flue-tribes taken together is 1339 square feet. The total weight of the engine in working order is 28 tons 6 cwt.; of which nearly 12 tons are driving weight, - the weight at the diiving-wheels. The tender stands on three pairs of wheels and weighs about 16 tons, with, in addition, 1780 gallons or 8 tons of water when filled, and 3 tons of coal.

The "Lady of the Lake " is an express passenger locomotive, one of a class which was designed by Mr John Ramsbottom with special regard to the running of express trains on the northern division of the London and North-Western Railway. The cylinders are " outside " ; they are 16 inehes in diameter, with 24 inches of stroke, and the driving-wheels are 7 feet 7 inches in diameter. The fire-grate has an area of 15 square feet, and there is over 1000 square feet .of heating surface. The engine weighs 27 tons in working order and the tender 17i, together 44i. tons. The tender is fitted with Air Ramsbottom's apparatus for picking up feed-water whilst running : a. scoop is let down from the bottom of the tender and dips into water contained in a long open trough. laid 13etween the rails, from which it is scooped up into the tanks. The minimum speed at v.-hich this operation can be effected is 22 miles per hour. By the aid of the water-lifter this express engine has been enabled to run the whole distance from Holyhead to London-264 miles - in onc continuous run, at an average speed of 42 miles per hour, taking a train of eight or nine carriages, and consuming 27 lb of coal as fuel per mile run.

An express passenger locomotive having 18-inch cylinders and four-coupled driving-wheels, 7 feet in diameter, with a four-wheel bogie in front under the smoke -box, was designed by Mr T. W. Johnson for the traffic of the Midland Railway. The engine stands on eight wheels, forming a base 21i feet long. It weighs about 42 tons in working order, and with the tender, including coal and water, about 68 tons. The average load taken by engines of this class is fourteen carriages at the time-bill speed of 50 miles per hour, over gradients of from 1 in 120 to 1 in 130, with a consump-tion of 28 itr of coal per mile run. The engine can take as a maxi-mum load seventeen carriages between Manchester and Derby, over ruling gradients of 1 in 90 and 1 in 100 for 10 miles, at a speed up the inclines of 35 miles per hour, and on levels and falling gradients at 50 miles per hour. The carriages weigh, with passengers, 11 tons each, making up a train of the gross v.-eight of 187 tons.

inches in diameter, and a single pair of 8-feet driving-wheels. It is one of the most recent developments of the single-wheel engine. It is placed on eight wheels, of which the first four are framed in a bop,ie, or truck, pivoted on a centre under the smoke-box. The cylinders are placed outside, and between the wheels of the bogie at each side. They are 18 inches in diameter, with a stroke of 28 inches, - dimensions which, taken together, exceed in magni-tude those of any other engine for English passenger-traffic. The driving-wheels are 8 feet 1 inch in diameter and the bogie-wheels 3 feet 11 inches. The engine weighs 38 tons in working order, the distribution of the weight being as follows : - Leading bogie-wheels 15 tons 7 tons Hind „ „ / 8 „ Driving-wheels 15 „ Hind wheels 8 „ Total weight in working order 38 „ The pivot of the bogie is 6 inches nearer the hind than the front axle, - these being 6i feet apart. By this disposition the• bogie appears to lead better than if the pivot were, as usual, equidistant between the axles. The working pressure in the boiler is 140 lb per square inch. There are 217 brass flue-tubes, IA- inches in diameter, presenting a heating surface for evaporation of upwards of 1000 square feet. There is in all 1165 square feet of surface, and there is 17.6 square feet of grate surface. Air Stirling, on the question of single-wheel versus coupled wheels for passenger locomotives, states that he constructed two classes of engines, - one class with four 6i-feet wheels coupled, the other with a single pair of 7-feet diiving- wheels. The boilers of the two classes were alike ; also the cylinders, which were 17 inches in diameter, with 24 inches of stroke. The pressure in the boilers was 140 lb. With like trains the single-wheel engine had the better of it ; in fact, it generally beat the coupled engine in time, running from King's Cross to Potter's Bar, a distance of nearly 13 miles, nearly all uphill, the gradients varying from 1 iu 105 for 2 miles to 1 in 200. Engines of the class of the 8-feet-wheel engine travel between King's Cross and Leeds or York. The steepest gradients on the route are met vvith on leaving Leeds, ascending 1 in 50, besides the gradient 1 in 105 leaving King's Cross. Trains of from sixteen to twenty-two carriages are taken from King's Cross station with ease ; and on several occasions twenty-eight carriages have been taken, and time has been kept. On one occasion a distance of 15 miles in.

twelve minutes was accomplished with a train of sixteen carriages, making a speed of 75 miles per hour. The engine has taken a train of thirty-three carriages full of passengers from Doncaster to Scarborough and back at an average speed of 45 miles per hour. It is capable of moving a gross weight, including engine, tender, and train, of 356 tons on a level at a speed of 45 miles per hour. The average results of the reg,ular performance of seven engines of this class between Doncaster, Peterborough, and London for the third quarter of 1884 show that a train of twelve six-Nvheeled carriages weighing 13 tons each was taken at a speed of from 50 to 53 miles per hour, for a consumption of 251 lb of coal per mile run and five pints of oil per 100 miles run.

Four-coupled locomotives, having the cylinders inside, and four wheels coupled " in front," with a pair of hind or trailing wheels, are known as "mixed engines," - that is to say, engines adapted for either passenger traffic or goods traffie, - a generally useful type. In one example the cylinders are 16 inches in diameter, with a stroke of 22 inches ; the coupled wheels are 5 feet in diameter. The weight of the engine is 241 tons, of which 20 tons are driving weight.

The next eng,ine to be noticed is a generally useful engine, four-coupled "behind," for passenger traffic, such, for instance, as that with inclined fire-gate and sloping fire-box designed by Mr J. J. Cudworth for service on the South-Eastern Railway. On a wheel-base of 15 feet the weight of the engine-301 tons - is so distributed that 101 tons fall at each pair of driving-wheels and 91 tons at the leading wheels. The cylinders are inside, 16 inches in diameter, with 24 inches of stroke and 6-feet driving-wheels.

Another express passenger locomotive, having inside cylinders and four-coupled wheels behind, for service on the London and North-Western Railway, has cylinders 17 inches in diameter, with 24 inches of stroke, and 6 feet 7 inch (hiving wheels. The engine weighs 291 tons, of which 11 are at the middle wheels, 8/ at the hind wheels, and 9/ at the front ; thus the driving weight amounts to two-thirds of the total weight. This engine can move a gross weight of 293 tons, comprising engine, tender, and train, on a level at a speed of 45 miles per hour, with a working pressure of 120 /b per square inch in the boiler. With trains averaging ten carriages the consumption of coal is 261 lb per nfile run.

A tank locomotive is an engine which carries its supply of fuel and water with it on its own frame, dispensing with the tender. Stich eng,ines are much used for short traffic, as well as for shunting and marshalling trains.

The four-coupled tank engine (fig. 41) used for the passenger traffic of the Metropolitan Railway has four wheels coupled behind and a bogie in front. This engine wei,ghs in workinr, order 451 tons, of which about 35 tons are utilized as drivin,g weiiht, making 171 tons for one pair of wheels, - about the greatest load on one pair of wheels anywhere. The regular duty of this engine is to take a train of six carriages capable of holding in all 432 passengers, and weighing in themselves 13 tons each, at an averaae speed, including stoppages, of 18 miles per hour, consuming37 tb of Welsh coal per train mile run. Whilst passing through the tunnels or covered ways the exhaust steam from the engine is condensed in large tanks carried on the engine, filled. with cold water. The cluantity of condensing water consumed is 900 gallons for half the Journey, or every' 61 miles ; it is raised to 200° Fahr. temperature.

The eight-wheeled tank engine (fig. 42) has been designed by- Mr T. W. Worsdell to work the heavy suburban metropolitan traffic of the Great Eastern Railway, - the ordinary trains in this service being composed of fifteen or twenty close-coupled carriages, .taken over steep gradients and sharp curves. For this purpose the fore and hind axles are radially- mounted, as before explained, to take the curves with facility, the engine running either end first. The eng,ine weighs 52 tons in working order, and of these 30 tons are driving weight placed on the two pairs of coupled driving-wheels. With large cylinders 18 inches in diameter, anti driving- wheels only 5 feet 4 inches in diameter, the engine is adapted for starting promptly, which it is required to do in order to keep time between closely placed stations. Every stop is made by the Westinghouse brake, with which the engine is fitted.

Locomotives for drawing heavy goods trains, thongh not hearier than the most powerful passenger locomotives, can take goods trains of great weight. Six-coupled goods engines, with 17-inch cylinders and driving-wheels 5 feet in diameter, weighing 32 tons in working order, can take a train weighing 360 tons on a level at a speed of 25 miles per hour, consuming from 40 to 45 tb of coal per mile run with trains. The Fairlie engine (fig. 43) is placed on two bogies or swivelling trucks, the foremost 'of which carries the cylinders and propelling gear and the hindmost the tank and coal-boxes.

The longest distance run without stopping, combined with the] highest speed, is performed on the Great Northern Railway, between S. Grantham and liing's Cross, 1051 miles, in 1 hour 58 minutes, at the rate of 531 miles per hour. The Great Western Company run from Paddington to Swindon-77/ miles - in 1 hour 27 minutes, being at the rate of 531 miles per hour. On the London and North-Western Railway the distance-771 miles - from Willesden to Rugby is run in 1 hour 2S minutes, at the rate of 52/ miles per hour. The average rate of express and mail passenger trains on this line is 40 miles per hour or more. Parliamentary trains, call-ing at all stations, run at an average speed of front 19 to 28 miles per hour. Express goods trains attain a speed of from 20 to 25 miles per hour. The speed of coal trains is limited, as far as possible, to 15 miles per hour.

The coal trains on tbe London and North-Western, Midland, and Great Northern Railways generally consist of from thirty to I thirty-five wag,gons, weighing from 5 to 51 tons each, and carry-ing a load of 8 tons of coal. At this rate the total load of coal for thirty-five waggons weighs 280 tons, and, adding the weight of tbe brake-ran at the end of the train, 10 tons 17 ewt., the maximum gross weight of train is 4S3 tons 7 cwt., as on the Great .Northern Railway. This train is taken by a goods engine with six-coupled wheels 51 feet in diameter, having two steam cylinders 171 inches in diameter, with a stroke of 26 inches, and a pressure of 140 lb per square inch in the boiler. The loco-motive weighs in working order 36 tons 18 cwt., and the tender with fuel and water 30 tons 17 cwt., making together 67 tons 15 cwt. for the locomotive and tender The gross weights are as follows : - Tons. cwts.

These large coal trains are taken at a speed of 18 miles per hour, on ascending inclines of 1 in 178 at 10 miles per hour. The con-sumption of coal as fuel in the engine is at the rate of 45 lb per mile run, including the coal consumed in getting up steam. Mr Patrick Stirling, the locomotive engineer of the Great Northern Railway, has also designed and constructed still more powerful engines, having six-coupled 5-feet wheels, with cylinders 19 inches in diameter and of 28 inches stroke These engines are capable of taking a train of forty-nine loaded coal-waggons, weighing with brake-van 6721 tons. Including the weight of the engine and tender the total gross load is, say, 740 tons, taken with a consump-tion of 50 M of coal per mile nth. This is probably the most extraordinary example of a dead pull on an ascending incline of 1 in 178. It is equivalent to a gross weight of 1816 tons on a level. It was found that this train was too long for some of the sidings, besides fouling both the level crossings in the city of Lincoln ; hence the train was reduced in number to forty-five waggons. Six-coupled goods-engines of the usual proportions, working at full power, exert a tractive force of from 5 to 6 tons in the direction of the rails, equal to the movement of a gross weight of engine, tender, and train of from 1240 to 1500 tons on a level straight line at a speed of 15 miles per hour, or to from 386 to 463 tons on a level straight line at a speed of 60 miles per hour. A tractive force of 10 or 12 th is capable of drawing 1 ton on a level at 10 miles per hour. At 60 miles per hour the required tractive force is about 45 It) for 1 ton of gross weight.