# 1911 Encyclopædia Britannica/Railways/Rolling Stock

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Rolling Stock
The rolling stock of a railway comprises those vehicles by means of which it effects the transportation of persons and things over its lines. It may be divided into two classes, according as it is intended for passenger or for goods traffic.
Passenger Train Stock.—In the United Kingdom, as in Europe generally, the vehicles used on passenger trains include first class carriages, second-class carriages, third-class carriages, composite carriages containing compartments for two or more classes of passengers, dining or restaurant carriages, sleeping ​carriages, mail carriages or travelling post offices, luggage brake vans, horse-boxes and carriage-trucks. Passenger carriages were originally modelled on the stage-coaches which they superseded, and they are often still referred to as “coaching stock.” Early examples had bodies about 15 ft. long, 6½ ft. wide and 4¾ ft. high; they weighed 3 or 4 tons, and were divided into three compartments holding six persons each, or eighteen in all.
The distinction into classes was made almost as soon as the railways began to carry passengers. Those who paid the highest fares (2½d. or 3d. a mile) were provided with covered vehicles, on the roofs of which their luggage was carried, and from the circumstance that they could book seats in advance came the term “booking office,” still commonly applied to the office where tickets are issued. Those who travelled at the cheaper rates had at the beginning to be content with open carriages having little or no protection from the weather. Gradually, however, the accommodation improved, and by the middle of the 19th century second-class passengers had begun to enjoy “good glass windows and cushions on the seat,” the fares they paid being about 2d. a mile. But though by an act of 1844 the railways were obliged to run at least one train a day over their lines, by which the fares did not exceed the “Parliamentary” rate of 1d. a mile, third-class passengers paying 1¼d. or 1½d. a mile had little consideration bestowed on their comfort, and were excluded from the fast trains till 1872, when the Midland railway admitted them to all its trains. Three years later that railway did away with second-class compartments and improved the third class to their level. This action had the effect, through the necessities of competition, of causing travellers in the cheaper classes to be better treated on other railways, and the condition of the third-class passenger was still further improved when Parliament, by the Cheap Trains Act of 1883, required the railways to provide “due and sufficient” train accommodation at fares not exceeding 1d. a mile. In the United Kingdom it is now possible to travel by every train, with very few exceptions, and in many cases to have the use of restaurant cars, for 1d. a mile or less, and the money obtained from third-class travellers forms by far the most important item in the revenue from passenger traffic. Since the Midland railway’s action in 1875 several other English companies have abandoned second-class carriages either completely or in part, and in Scotland they are entirely unknown.
On the continent of Europe there are occasionally four classes, but though the local fares are often appreciably lower than in Great Britain, only first and second class, sometimes only first class, passengers are admitted to the fastest trains, for which in addition a considerable extra fare is often required. In Hungary and Russia a zone-tariff system is in operation, whereby the charge per mile decreases progressively with the length of the journey, the traveller paying according to the number of zones he has passed through and not simply according to the distance traversed. In the United States there is in most cases nominally only one class, denominated first class, and the average fare obtained by the railways is about 1d. per mile per passenger. But the extra charges levied for the use of parlour, sleeping and other special cars, of which some of the best trains are exclusively composed, in practice constitute a differentiation of class, besides making the real cost of travelling higher than the figures just given.
In America and other countries where distances are great and passengers have to spend several days continuously in a Restaurant and sleeping cars.train sleeping and restaurant cars are almost necessity, and accordingly are to be found on most important through trains. Such cars in the United States are largely owned, not by the railway companies over whose lines they run, but by the Pullman Car Company, which receives the extra fees paid by passengers for their use. Similarly in Europe they are often the property of the International Sleeping Car Company (Compagnie Internationale des Wagons-Lits), and the supplementary fares required from those who travel in them add materially to the cost of a journey. In the United Kingdom, where the distances are comparatively small, sleeping and dining cars must be regarded rather as luxuries; still even so, they are to be met with very frequently. The first dining car in England was run experimentally by the Great Northern railway between London and Leeds in 1879, and now such vehicles form a common feature on express trains, being available for all classes of passengers without extra charge beyond the amount payable for food. The introduction of corridor carriages, enabling passengers to walk right through the trains, greatly increased their usefulness. The first English sleeping cars made their appearance in 1873, but they were very inferior to the vehicles now employed. In the most approved type at the present time a passage runs along one side of the car, and off it open a number of transverse compartments or berths resembling ships' cabins, mostly for one person only, and each having a lavatory of its own with cold, and sometimes hot, water laid on. A charge of 7s. 6d. or 10s., according to distance, is made for each bed, in addition to the first-class fare. In the United States the standard sleeping car has a central alley, and along the sides are two tiers of berths, arranged lengthwise with the car and screened off from the alley by curtains. To some extent cars divided into separate compartments are also in use in that country. On the continent of Europe the typical sleeping car has transverse compartments with two berths, one placed above the other.
The first railway carriages in England had four wheels with two axles, and this construction is still largely employed, Passenger carriages.especially for short-distance trains. Later, when increased length became desirable, six wheels with three axles came into use; vehicles of this kind were made about 30 ft. long, and contained four compartments for first-class passengers or five for second or third class, carrying in the latter case fifty persons. Their weight was in the neighbourhood of 10 tons. In both the four-wheeled and the six-wheeled types the axles were free to rise and fall on springs through a limited range, but not to turn with respect to the body of the carriage, though the middle axle of the six-wheeled coach was allowed a certain amount of lateral play. Thus the length of the body was limited, for to increase it involved an increase in the length of the rigid wheel base, which was incompatible with smooth and safe running on curves. (On the continent of Europe, however, six-wheeled vehicles are to be found much longer than those employed in Great Britain.) This difficulty is avoided by providing the vehicles with four axles (or six in the case of the largest and heaviest), mounted in pairs (or threes) at each end in a bogie or swivel truck, which being pivoted can move relatively to the body and adapt itself to the curvature of the line. This construction was introduced into England from America about 1874, and has since been extensively adopted, being now indeed standard for main line stock. It soon led to an increase in the length of the vehicles; thus in 1885 the Midland railway had four-wheeled bogie third-class carriages with bodies 43 ft. long, holding seventy persons in seven compartments and weighing nearly 18 tons, and six wheeled bogie composite carriages, 54 ft. long and weighing 23 tons, which included 3 first-class and 4 third-class compartments, with a cupboard for luggage, and held 58 passengers. The next advance, introduced on the Great Western railway in 1892, was the adoption of corridor carriages having a passage along one side, off which the compartments open, and connected to each other by vestibules, so that it is possible to pass from one end of the train to the other. This arrangement involves a further increase of length and weight. For instance, four wheeled bogie third-class corridor carriages employed on the Midland railway at the beginning of the 20th century weighed nearly 25 tons, and had bodies measuring 50 ft.; yet they held only 36 passengers, because not only had the number of compartments been reduced to six, as compared with seven in the somewhat shorter carriage of 1885, by the introduction of a lavatory at each end, but each compartment held only 6 persons, instead of 10, owing to the narrowing of its width by the corridor.
​It will be seen from these particulars—which are typical of what has happened not only on other British railways, but also on those of other countries—that much more space has to be provided and more weight hauled for each passenger than was formerly the case. Thus, on the Midland railway in 1885, each third-class passenger, supposing the carriage to have its full complement, was allowed 0·62 ft. of lineal length, and his proportion of the total weight was 5·7 cwt. Less than 20 years later the lineal length allowed each had increased to nearly 1·4 ft., and the weight to nearly 14 cwt. Passengers in sleeping cars appropriate still more space and weight; in Great Britain some of these cars, though 40 tons in weight and over 65 ft. in length, accommodate only 11 sleepers, each of whom thus occupies nearly 6 ft. of the length and requires over 3½ tons of dead weight to be hauled.
In America the long open double-bogie passenger cars, as originally introduced by Ross Winans on the Baltimore & Ohio railway, are universally in use. They are distinguished essentially from the British type of carriage by having in the centre of the body a longitudinal passage, about 2 ft. wide, which runs their whole length, and each car having communication with those on either side of it, the conductor, and also vendors of books, papers and cigars, are enabled to pass right through the train. The cars are entered by steps at each end, and are provided with lavatories and a supply of iced water. The length is ordinarily about 50 ft., but sometimes 80 or 90 ft. The seats, holding two persons, are placed transversely on each side of the central passage, and have reversible backs, so that passengers can always sit facing the direction in which the train is travelling. Cars of this saloon type have been introduced into England for use on railways which have adopted electric traction, but owing to the narrower loading gauge of British railways it is not usually possible to seat four persons across the width of the car for its whole length, and at the ends the seats have to be placed along the sides of the vehicle. A considerable amount of standing room is then available, and those who have to occupy it have been nicknamed “strap hangers,” from the fact that they steady themselves against the motion of the train by the aid of leather straps fixed from the roof for that purpose. Cars built almost entirely of steel, in which the proportion of wood is reduced to a minimum, are used on some electric railways, in order to diminish danger from fire, and the same mode of construction is also being adopted for the rolling stock of steam railways.
End doors opening on end platforms have always been characteristic of American passenger equipment. Their use Vestibules.secures a continuous passageway through the train, but is attended with some discomfort and risk when the train is in motion. The opening of the doors was apt to cause a disagreeable draught through the car in cold weather, and passengers occasionally fell from the open platform, or were blown from it, when the train was moving. To remedy these defects vestibules were introduced, to enclose the platform with a housing so arranged as to be continuous when the cars are made up into trains, and fitted with side doors for ingress and egress when the trains are standing. A second advantage of the vestibule developed in use, for it was found that the lateral swaying of the cars was diminished by the friction between the vestibule frames. The fundamental American vestibule patent, issued to H. H. Sessions of Chicago in November 1887, covered a housing in combination with a vertical metallic plate frame of the general contour of the central passage-way, which projected slightly beyond the line of the couplings and was held out by horizontal springs top and bottom, being connected with the platform housing by flexible connexions at the top and sides and by sliding plates below. A common form is illustrated in fig. 27. Subsequent improvements on the Sessions patent have resulted in a modified form of vestibule in which the housing is made the full width of the platform, though the contact plate and springs and the flexible connexions remain the same as before. The application of vestibules is practically limited to trains making long journeys, as it is an obstruction to the free ingress and egress of passengers on local trains that make frequent stops.
Fig. 27.—A “Vestibule”; the “lazy tongs” gate is folded away when two cars are coupled together, giving free passage from end to end of the train.
In the United States the danger of the stoves that used to be employed for heating the interiors of the cars has been Heating and lighting.realized, and now the most common method is by steam taken from the locomotive boiler and circulated through the train in a line of piping, rendered continuous between the cars by flexible coupling-hose. The same method is finding increased favour in Great Britain, to the super session of the old hot-water foot warmers. These in their simplest form are cans filled with water, which is heated by immersing them in a vessel containing boiling water. In some cases, however, they are filled with fused acetate of soda; this salt is solid when cold, but when the can containing it is heated by immersion in hot water it liquefies, and in the process absorbs heat which is given out again on the change of state back to solid. Such cans remain warm longer than those containing only hot water. On electric railways the trains are heated by electric heaters. As to lighting, the oil lamp has been largely displaced by gas and electricity. The former is often a rich oil-gas, stored in steel reservoirs under the coaches at a pressure of six or seven atmospheres, and passed through a reducing valve to the burners; these used to be of the ordinary fish-tail type, but inverted incandescent mantles are coming into increasing use. Gas has the disadvantage that in case of a collision its inflammability may assist any fire that may be started. Electric light is free from this drawback. The current required for it is generated by dynamos driven from the axles of the coaches. With “set” or “block” trains, that is, trains having their vehicles permanently coupled up, one dynamo may serve for the whole train, but usually a dynamo is provided for each coach, which is then an ​independent unit complete in itself. It is necessary that the voltage of the current shall be constant whatever be the increase of the speed of the train, and therefore of the dynamo. In most of the systems that have been proposed this result is attained by electrical regulation; in one, however, a mechanical method is adopted, the dynamo being so hung that it allows the driving belt to slip when the speed of the axle exceeds a certain limit, the armature thus being rotated at an approximately constant speed. In all the systems accumulators are required to maintain the light when the train is at rest or is moving too slowly to generate current.
In all countries passenger trains must vary in weight according to the different services they have to perform; suburban Weight and speed.trains, for example, meant to hold as many passengers as possible, and travelling at low speeds, do not weigh so much as long-distance expresses, which include dining and sleeping cars, and on which, from considerations of comfort, more space must be allowed each occupant. The speed at which the journey has to be completed is obviously another important factor, though the increased power of modern locomotives permits trains to be heavier and at the same time to run as fast, and often faster, than was formerly possible, and in consequence the general tendency is towards increased weight as well as increased speed. An ordinary slow suburban train may weigh about 100 tons exclusive of the engine, and may be timed at an inclusive speed, from the beginning to the end of its journey, as low as 12 or 15 m. an hour; while usually the fastest express trains maintaining inclusive speeds of say 45 m. an hour, and made up of the heaviest and strongest rolling stock, do not much exceed 300 tons in any country, and are often less. The inclusive speed over a long journey is of course a different thing from the average running speed, on account of the time consumed in intermediate stops; the fewer the stops the more easily is the inclusive speed increased,—hence the advantage of the non-stop runs of 150 and 200 m. or more which are now performed by several railways in Great Britain, and on which average speeds of 54 or 55 m. per hour are attained between stopping-places. Over shorter distances still more rapid running is occasionally arranged, and in Great Britain, France and the United States there are instances of trains scheduled to maintain an average speed of 60 m. an hour or more between stops. Still higher speeds, up to 75 or even 80 m. an hour, are reached, and sustained for shorter or longer distances every day by express trains whose average speed between any two stopping places is very much less. But isolated examples of high speeds do not give the traveller much information as to the train service at his disposal, for on the whole he is better off with a large number of trains all maintaining a good average of speed than with a service mostly consisting of poor trains, but leavened with one or two exceptionally fast ones. If both the number and the speed of the trains be taken into account, Great Britain is generally admitted still to remain well ahead of any other country.
Goods Trains.—The vehicles used for the transportation of goods are known as goods wagons or trucks in Great Britain, and as freight cars in America. The principal types to be found in the United Kingdom and on the continent of Europe are open wagons (the lading often protected from the weather by tarpaulin sheets), mineral wagons, covered or box wagons for cotton, grain, &c., sheep and cattle trucks, &c. The principal types of American freight cars are box cars, gondola cars, coal cars, stock cars, tank cars and refrigerator cars, with, as in other countries, various special cars for special purposes. Most of these terms explain themselves. The gondola or flat car corresponds to the European open wagons and is used to carry goods not liable to be injured by the weather; but in the United States the practice of covering the load with tarpaulins is unknown, and therefore the proportion of box cars is much greater than in Europe. The long hauls in the United States make it specially important that the cars should carry a load in both directions, and so box cars which have carried grain or merchandise one way are filled with wool, coal, coke, ore, timber and other coarse articles for the return journey. On this account it is common to put small end doors in American box cars, through which timber and rails may be loaded.
The fundamental difference between American freight cars and the goods wagons of Europe and other lands is in carrying capacity. In Great Britain the mineral trucks can ordinarily hold from 8 to 10 tons (long tons, 2240 ℔), and the goods trucks rather less, though there are wagons in use holding 12 or 15 tons, and the specifications agreed to by the railway companies associated in the Railway Clearing House permit private wagon owners (who own about 45% of the wagon stock run on the railways of the United Kingdom) to build also wagons holding 20, 30, 40 and 56 tons. On the continent of Europe the average carrying capacity is rather higher; though wagons of less than 10 tons capacity are in use, many of those originally rated at 10 tons have been rebuilt to hold 15, and the tendency is towards wagons of 15–20 tons as a standard, with others for special purposes holding 40 or 45 tons.
The majority of the wagons referred to above are comparatively short, are carried on four wheels, and are often made of wood. American cars, on the other hand, have long bodies mounted on two swivelling bogie-trucks of four wheels each, and are commonly constructed of steel. About 1875 their average capacity differed little from that of British wagons of the present day, but by 1885 it had grown to 20 or 22 short tons (2000 ℔) and now it is probably at least three times that of European wagons. For years the standard freight cars have held 60,000 ℔ and now many carry 80,000 ℔ or 100,000 ℔; a few coal cars have even been built to contain 200,000 ℔. This high carrying capacity has worked in several ways to reduce the cost of transportation. An ordinary British 10-ton wagon often weighs about 6 tons empty, and rarely much less than 5 tons; that is, the ratio of its possible paying load to its tare weight is at the best about 2 to 1. But an American car with a capacity of 100,000 ℔ may weigh only 40,000 ℔, and thus the ratio of its capacity to its tare weight is only about 5 to 2. Hence less dead weight has to be hauled for each ton of paying load. In addition the increased size of the American freight car has diminished the interest on the first cost and the expenses of maintenance relatively to the work done; it has diminished to some extent the amount of track and yard room required to perform a unit of work; it has diminished journal and rolling friction relatively to the tons hauled, since these elements of train resistance grow relatively less as the load per wheel rises; and finally, it has tended to reduce the labour costs as the train loads have become greater, because no more men are required to handle a heavy train than a light one.
It is sometimes argued that if these things are true for one country they must be true for another, and that in Great Britain, for example, the use of more capacious cars would bring down the cost of carriage. It may be pointed out, however, that the social and geographical conditions are different in the United Kingdom and the United States, and in each country the methods of carrying goods and passengers have developed in accordance with the requirements of those conditions. In the one country the population is dense, large towns are numerous and close to one another, the greatest distances to be travelled are short, and relatively a large part of the freight to be carried is merchandise and manufactured material consigned in small quantities. In the other country precisely the opposite conditions exist. Under the first set of conditions quickness and flexibility of service are relatively more important than under the second set. Goods therefore are collected and dispatched promptly, and, to secure rapid transit, are packed in numerous wagons, each of which goes right through to its destination, with the consequence that, so far as general merchandise is concerned, the weight carried in each is a quarter or less of its capacity. But if full loads cannot be arranged for small wagons, there is obviously no economy in introducing larger ones. On the other hand, where, as in America, the great ​volume of freight is raw material and crude food-stuffs, and the distances are great, a low charge per unit of transportation is more important than any consideration such as quickness of delivery; therefore full car-loads of freight are massed into enormous trains, which run unbroken for distances of perhaps 1000 m. to a seaport or distributing centre.
The weight and speed of goods trains vary enormously according to local conditions, but the following figures, which refer to traffic on the London & North-Western railway between London and Rugby, may be taken as representative of good English practice. Coal Weight and speed.trains, excluding the engine, weigh up to 800 or 900 tons, and travel at from 18 to 22 m. an hour; ordinary goods or merchandise trains, weighing 430 tons, travel at from 25 to 30 m. an hour; and quick merchandise trains with limited loads of 300 tons make 35 to 40 m. an hour. In the United States mineral and grain trains, running at perhaps 12 m. an hour, may weigh up to about 4000 tons, and loads of 2000 tons are common. Merchandise trains run faster and carry less. Their speed must obviously depend greatly on topographical conditions. In the great continental basin there are long lines with easy gradients and curves, while in the Allegheny and Rocky Mountains the gradients are stiff, and the curves numerous and of short radius. Such trains, therefore, range in weight from 600 to 1800 tons or even more, and the journey speeds from terminus to terminus, including stops, vary from 15 to 30 m. an hour, the rate of running rising in favourable circumstances to 40 or even 60 m. an hour.
Couplers.—The means by which vehicles are joined together into trains are of two kinds—automatic and non-automatic, the difference between them being that with the former the impact of two vehicles one on the other is sufficient to couple them without any human intervention such as is required with the latter. The common form of non-automatic coupler, used in Great Britain for goods wagons, consists of a chain and hook; the chain hangs loosely from a slot in the draw-bar, which terminates in a hook, and coupling is effected by slipping the chain of one vehicle over the hook of the next. For this operation, or its reverse, a man has to go in between the wagons, unless, as in Great Britain, he is provided with a coupling-stick—that is, a pole having a peculiarly shaped hook at one end by which the chain can be caught and thrown on or off the drawbar hook. This coupling gear is placed centrally between a pair of buffers; formerly these were often left “dead”—that is, consisted of solid prolongations of the frame of the vehicle, but now they are made to work against springs which take up the shocks that occur when the wagons are thrown violently against one another in shunting. In British practice the chains consist of three links, and are of such a length that when fully extended there is a space of a few inches between opposing buffers; this slack facilitates the starting of a heavy train, since the engine is able to start the wagons one by one and the weight of the train is not thrown on it all at once. For passenger trains and occasionally for fast goods trains screw couplings are substituted for the simple chains. In these the central bar which connects the two end links has screw threads cut upon it, and by means of a lever can be turned so as either to shorten the coupling and bring the vehicles together till their buffers are firmly pressed together, or to lengthen it to permit the end link to be lifted off the hook.
Another form of coupler, which used to be universal in the United States, though it has now been almost entirely superseded by the automatic coupler, was the “link and pin,” which differed fundamentally from the couplers commonly used in Europe, in the fact that it was a buffer as well as a coupler, no side buffers being fitted. In it the draw-bar, connected through a spring to the frame of the car, had at its outboard end a socket into which one end of a solid link was inserted and secured by a pin. The essential change from the link and pin to the automatic coupler is in the outboard end or head of the draw-bar. The socket that received the link is replaced by a hook, shown at A in fig. 28, which is usually called the knuckle. This hook swings on the pivot B, and has an arm which extends backwards, practically at right angles with the working face of the hook, in a cavity in the head, and engages with the locking-pin C. This locking-pin is lifted by a suitable lever which extends to one or both sides of the car; lifting it releases the knuckle, which is then free to swing open, disconnecting the two cars. The knuckle stands open until the coupling is pushed against another coupling, when the two hooks turn on their pivots to the position shown in fig. 28, and, the locking-pin dropping into place, the couplers are made fast. This arrangement is only partly automatic, since it often happens that when two cars are brought together to couple the knuckles are closed and must be opened by hand. There are various contrivances by which this may be done by a man standing clear of the cars, but often he must go in between their ends to reach the knuckle.
Fig. 28.—Automatic Coupling for Freight Cars (U.S.A.).
This form of automatic coupler has now gained practically universal acceptance in the United States. To effect this result required many years of discussion and experiment. The Master Car Builders’ Association, a great body of mechanical officers organized especially to being about improvement and uniformity in details of construction and operation, expressed its sense of the importance of “self-coupling” so far back as 1874, but no device of the kind that could be considered useful had then been invented. At that time a member of the Association referred to the disappearance of automatic couplers which had been introduced thirty or forty years before. This body pursued the subject with more or less diligence, and in 1884 laid down the principle that the automatic coupler should be one acting in a vertical plane-that is, the engaging faces should be free to move up and down within a considerable range, in order to provide for the differences in the height of cars. By the fixing of this principle the task of the inventor was considerably simplified. In 1887 a committee reported that the coupler question was the “knottiest mechanical problem that had ever been presented to the railroad,” and over 4000 attempted solutions were on record in the United States Patent Office. The committee had not found one that did not possess grave disadvantages, but concluded that the “principle of contact of the surfaces of vertical surfaces embodied in the Janney coupler afforded the best connexion for cars on curves and tangents”; and in 1887 the Association recommended the adoption of a coupler of the Janney type, which, as developed later, is shown in fig. 28. The method of constructing the working faces of this coupler is shown in fig. 29. The principle was patented, but the company owning the patent undertook to permit its free use by railway companies which were members of the Master Car Builders’ Association, and thus threw open the underlying principle to competition. From that time the numerous patents have had reference merely to details. Many different couplers of the Janney type are patented and made by different firms, but the tendency is to equip new cars with one of only four or five standard makes. The adoption of automatic couplers was stimulated in some degree by laws enacted by the various states and by the United States; and the Safety Appliance Act passed by Congress in 1893 made it unlawful for railways to permit to be hauled on their lines after the 1st of January 1898 any car used for interstate commerce that was not equipped with couplers which coupled automatically by impact, and which could be uncoupled without the necessity for men going in between the ends of the cars. The limit was extended to the 1st of August 1900 by the Interstate Commerce Commission, which was given discretion in the matter.
​Automatic couplers resembling the Janney are adopted in a few special cases in Great Britain and other European countries, but the great majority of couplings remain non-automatic. It may be pointed out that the general employment of side buffers in Europe greatly complicates the problem of designing a satisfactory automatic coupling, while to do away with them and substitute the combined buffer-coupling, such as is used in the United States, would entail enormous difficulties in carrying on the traffic during the transition stage.
* Fig. 29.—Development of the Working Faces of the Janney Coupler. The sides of the square are 6 in., and the centres AA are taken at 2 in. from the top and bottom of the square. The circles A′A′, which are struck with 2-inch radius, define the first portion of the knuckle. The inner circle B has a radius of 1½ in. From its intersection with A′A′ arcs are struck cutting B in two points. These intersections determine the centres of the semicircles CC which form the ends of the respective knuckles. These semicircles and the circles A′A′ are joined by tangents and short arcs struck from the centre of the figure.
Brakes.—In the United States the Safety Appliance Act of 1893 also forbade the railways, after the 1st of January 1898, to run trains which did not contain a “sufficient number” of cars equipped with continuous brakes to enable the speed to be controlled from the engine. This law, however, did not serve in practice to secure so general a use of power brakes on freight trains as was thought desirable, and another act was passed in 1903 to give the Interstate Commerce Commission authority to prescribe what should be the minimum number of power-braked cars in each train. This minimum was at first fixed at 50%, but on and after the 1st of August 1906 it was raised to 75%, with the result that soon after that date practically all the rolling stock of American railways, whether passenger or freight, was provided with compressed air brakes. In the United Kingdom the Regulation of Railways Act 1889 empowered the Board of Trade to require all passenger trains, within a reasonable period, to be fitted with automatic continuous brakes, and now all the passenger stock, with a few trifling exceptions, is provided with either compressed-air or vacuum brakes (see Brake), and sometimes with both. But goods and mineral trains so fitted are rare, and the same is the case on the continent of Europe, where, however, such brakes are generally employed on passenger trains.  (H. M. R.)