Chapter V (2)

This Niagara railway suspension bridge has been so long in successful operation that it is difficult now to appreciate the general disbelief in the possibility of its success as a railway bridge, when it was undertaken. It was projected and executed by the late John A. Roebling. Before it was finished, Robert Stephenson said to him, "If your bridge succeeds, mine is a magnificent blunder." The Niagara bridge did succeed.

From a painting by J. H. Twachtman.]

We are so familiar with the great suspension bridge between New York and Brooklyn, that only a simple statement of some of its characteristic features will be given. Its clear span is 1,595½ feet. With its approaches its length is 3,455 feet. The clear waterway is 135 feet high. The towers rise 272 feet above high water and extend on the New York side down to rock 78 feet below. The four suspension cables are of steel wire and support six parallel steel trusses, thus providing two carriage ways, two lines of railway, and one elevated footway. The cables are carried to bearing anchorages in New York and in Brooklyn. The cars on the bridge are propelled by cables, and the amount of travel is now so great as to demand some radical changes in the methods for its accommodation, which a few years ago were supposed to be ample.

Except under special circumstances of location or length of span, the truss bridge is a more economical and suitable structure for railway traffic than a suspension bridge.

The advance from the wood truss to the modern steel structure has been through a number of stages. Excellent bridges were built in combinations of wood and iron, and are still advocated where wood is inexpensive. Then came the use of cast iron for those portions of the truss subject only to compressive strains, wrought iron being used for all members liable to tension. Many bridges of notable spans were built in this way and are still in use. The form of this combination truss varied with the designs of different engineers, and the spans extended to over three hundred feet. The forms bore the names of the designers, and the Fink, the Bollman, the Pratt, the Whipple, the Post, the Warren, and others had each their advocates. The substitution of wrought for cast iron followed, and until quite recently trusses built entirely of wrought iron have been used for all structures of great span. The latest step has been made in the use of steel, at first for special members of a truss and latterly for the whole structure. The art of railway bridge building has thus, in a comparatively few years, passed through its age of wood, and then of iron, and now rests in the application of steel in all its parts.

Two distinct ways of connecting the different parts of a structure are in common use, riveting and pin connections.

In riveted connections the various parts of the bridge are fastened at all junctions by overlapping the plates of iron or steel and inserting rivets into holes punched through all the plates to be connected. The rivets are so spaced as to insure the best result as to strength. The pieces of metal are brought together, either in the shop or at the structure during erection, and the rivets, which are round pieces of metal with a head formed on one end, are heated and inserted from one side, being made long enough to project sufficiently to give the proper amount of metal for forming the other head. This is done while the rivet is still hot, either by hammering or by the application of a riveting machine, operated by steam or hydraulic pressure. Ingenious portable machines are now manufactured which are hung from the structure during erection and connected by flexible hose with the steam power, by the use of which the rivet heads can be formed in place with great celerity. The connections of plates by rivets of proper dimensions and properly spaced give great strength and stiffness to such joints.

In pin connections the members of a structure are assembled at points of junction and a large iron or steel pin inserted in a pin-hole running through all the members. This pin is made of such diameter as to withstand and properly transmit all the strains brought upon it. Joints made with such pin connections have flexibility, and the strains and stresses can be calculated with great precision. Eye-bars are forged pieces of iron or steel, generally flat, and enlarged at the ends so as to give a proper amount of metal around the pin-hole or eye, formed in those ends.

Structures connected by pins at their principal junctions have, of course, many parts in which riveting must be used.

The elements which are distinctively American in our railway bridges are the concentration of material in few members and the use of eye-bars and pin connections in place of riveted connections. The riveted methods are, however, largely used in connection with the American forms of truss construction.

An excellent example of an American railway truss bridge is shown on the opposite page. This structure spans the Missouri River at its crossing by the Northern Pacific Railroad. It has three through spans of 400 feet each and two deck spans of 113 feet each. The bottom chords of the long spans are 50 feet above high water, which at this place is 1,636 feet above the level of the sea. The foundations of the masonry piers were pneumatic caissons. The trusses of the through spans, 400 feet long, are 50 feet deep and 22 feet between centres. They are divided into 16 panels of 25 feet each. The truss is of the double system Whipple type, with inclined end posts. The bridge is proportioned to carry a train weighing 2,000 pounds per lineal foot, preceded by two locomotives weighing 150,000 pounds in a length of 50 feet. The pins connecting the members of the main truss are 5 inches in diameter.

This bridge is a characteristic illustration of the latest type of American methods. The extreme simplicity of its lines of construction, the direct transfer of the strains arising from loads, through the members, to and from the points where those strains are concentrated in the pin connections at the ends of each member, are apparent even to the untechnical eye. The apparent lightness of construction arising from the concentration of the material in so small a number of members, and the necessarily great height of the truss, give a grace and elegance to the structure, and suggest bold and fine development of the theories of mechanics.

An interesting viaduct is shown in the above illustration, where the railway crosses its own line on a curved truss.

The truss bridges which have been mentioned as types of the modern railway bridge are erected by the use of false works of timber, placed generally upon piling or other suitable foundation, between the piers or abutments, and made of sufficient strength to carry each span of the permanent structure until it is completed and all its parts connected, or, as is technically said, until the span is swung. Then the false works are removed and the span is left without intermediate support. But there are places where it would be impossible or exceedingly expensive to erect any false works. A structure over a valley of great depth, or over a river with very rapid current, are instances of such a situation.

A suspension bridge would solve the problem, but in many cases not satisfactorily. The method adopted by Colonel C. Shaler Smith at the Kentucky River Bridge [p. 55] shows ingenuity and boldness worthy of special remark. The Cincinnati Southern Railroad had here to cross a cañon 1,200 feet wide and 275 feet deep. The river is subject to freshets every two months, with a range of 55 feet and a known rise of 40 feet in a single night. Twenty years before, the towers for a suspension bridge had been erected at this point. The design adopted for the railroad bridge was based upon the cantilever principle. The structure has three spans of 375 feet each, carrying a railway track at a height of 276 feet above the bed of the river. At the time of its construction this was the highest railway bridge in the world, and it is still the highest structure of the kind with spans of over 60 feet in length. The bridge is supported by the bluffs at its ends and by two intermediate iron piers resting upon bases of stone masonry. Each iron pier is 177 feet high, and consists of four legs, having a base of 71½ × 28 feet, and terminating at its top in a turned pin 12 inches in diameter under each of the two trusses. Each iron pier is a structure complete in itself, with provision for expansion and contraction in each direction through double roller beds interposed between it and the masonry, and is braced to withstand a gale of wind that would blow a loaded freight-train bodily from the bridge.

The trusses were commenced by anchoring them back to the old towers, and were then built out as cantilevers from each bluff to a distance of one-half the length of the side spans, and at this point rested upon temporary wooden supports. Thence they were again extended as cantilevers until the side spans were completed and rested upon the iron piers. This cantilever principle is simply the balancing of a portion of the structure on one side of a support by the portion on the opposite side of the same support. Similarly the halves of the middle span were built out from the piers, meeting with exactness in mid-air. The temporary support used first at the centre of one side span and then at the other, was the only scaffolding used in erecting the structure, none whatever being used for the middle span.

When the junction was made at the centre of the middle span, the trusses were continuous from bluff to bluff, and, had they been left in this condition, would have been subjected to constantly varying strains resulting from the rise and fall of the iron piers due to thermal changes. This liability was obviated by cutting the bottom chords of the side spans and converting them into sliding joints at points 75 feet distant from the iron piers. This done, the bridge consists of a continuous girder 525 feet long, covering the middle span of 375 feet, and projecting as cantilevers for 75 feet beyond each pier, each cantilever supporting one end of a 300-foot span, which completes the distance to the bluff on each side.

A most interesting example of cantilever construction is the railway bridge built several years ago at Niagara, only a few rods from the suspension bridge and a short distance below the great falls. It is shown in the illustrations above and on page 91. The floor of the bridge is 239 feet above the surface of the water, which at that point has a velocity in the centre of 16½ miles per hour and forms constant whirlpools and eddies near the shores. The total length of the structure is 910 feet, and the clear span over the river between the towers is 470 feet. The shore arms of the cantilever, that is to say, those portions of the structure which extend from the top of the bank to the top of the tower built from the foot of the bank, are firmly anchored at their shore ends to a pier built upon the solid rock. These shore-arms were constructed on wooden false works, and serve as balancing weights to the other or river arms of the lever, which project out over the stream. These river-arms were built by the addition of metal, piece by piece, the weight being always more than balanced by the shore-arms. The separate members of the river-arms were run out on the top of the completed part and then lowered from the end by an overhanging travelling derrick, and fastened in place by men working upon a platform suspended below. This work was continued, piece by piece, until the river-arm of each cantilever was complete, and the structure was then finished by connecting these river-arms by a short truss suspended from them directly over the centre of the stream. This whole structure was built in eight months, and is an example both of a bold engineering work and of the facility with which a pin-connected structure can be erected. The materials are steel and iron. The prosecution of this work by men suspended on a platform, hung by ropes from a skeleton structure projecting, without apparent support, over the rushing Niagara torrent, was always an interesting and really thrilling spectacle.

The Lachine Bridge recently built over the St. Lawrence near Montreal, illustrated below, has certain peculiar features. It has a total length of 3,514 feet. The two channel spans are each 408 feet in length and are through spans. The others are deck spans. Through spans are those where the train passes between the side trusses. Deck spans are those where the train passes over the top of the structure. These two channel spans and the two spans next them form cantilevers, and the channel spans were built out from the central pier and from the adjacent flanking spans without the use of false works in either channel. A novel method of passing from the deck to the through spans has been used, by curving the top and bottom chords of the channel spans to connect with the chords of the flanking spans. The material is steel.

This structure, light, airy, and graceful, forms a strong contrast to the dark, heavy tube of the Victoria Bridge just below.

The enormous cantilever Forth Bridge, with its two spans of 1,710 feet each, is in steady progress of construction and will when completed mark a long step in advance in the science of bridge construction.

Of entirely different design and principle from all these trusses are the beautiful steel arches of the St. Louis Bridge [p. 95], the great work of that remarkable genius, James B. Eads. This structure spans the Mississippi at St. Louis. Difficult problems were presented in the study of the design for a permanent bridge at that point. The river is subject to great changes. The variation between extreme low and high water has been over 41 feet. The current runs from 2¾ to 8½ miles per hour. It holds always much matter in suspension, but the amount so held varies greatly with the velocity. The very bed of the river is really in constant motion. Examination by Captain Eads in a diving-bell showed that there was a moving current of sand at the bottom, of at least three feet in depth. At low water, the velocity of the stream is small and the bottom rises. When the velocity increases, a "scour" results and the river-bed is deepened, sometimes with amazing rapidity. In winter the river is closed by huge cakes of ice from the north, which freeze together and form great fields of ice.

It was decided to be necessary that the foundations should go to rock, and they were so built. The general plan of the superstructure, with all its details, was elaborated gradually and carefully, and the result is a real feat of engineering. There are three steel arches, the centre one having a span of 520 feet and each side arch a span of 502 feet. Each span has four parallel arches or ribs, and each arch is composed of two cylindrical steel tubes, 18 inches in exterior diameter, one acting as the upper and the other as the lower chord of the arch. The tubes are in sections, each about twelve feet long, and connected by screw joints. The thickness of the steel forming the tubes runs from 1-3/16 to 2-1/8 inches. These upper and lower tubes are parallel and are 12 feet apart, connected by a single system of diagonal bracing. The double tracks of the railroad run through the bridge adjacent to the side arches at the elevation of the highest point of the lower tube. The carriage road and footpaths extend the full width of the bridge and are carried, by braced vertical posts, at an elevation of twenty-three feet above the railroad. The clear headway is 55 feet above ordinary high water. The approaches on each side are masonry viaducts, and the railway connects with the City Station by a tunnel nearly a mile in length. The illustration shows vividly the method of erection of these great tubular ribs. They were built out from each side of a pier, the weight on one side acting as a counterpoise for the construction on the other side of the pier. They were thus gradually and systematically projected over the river, without support from below, till they met at the middle of the span, when the last central connecting tube was put in place by an ingenious mechanical arrangement, and the arch became self-supporting.

The double arch steel viaduct recently built over the Harlem Valley in the city of New York [p. 97] has a marked difference from the St. Louis arches in the method of construction of the ribs. These are made up of immense voussoirs of plate steel, forming sections somewhat analogous to the ring stones of a masonry arch. These sections are built up in the form of great I beams, the top and bottom of the I being made by a number of parallel steel plates connected by angle pieces with the upright web, which is a single piece of steel. The vertical height of the I is 13 feet. The span of each of these arches is 510 feet. There are six such parallel ribs in each span, connected with each other by bracing. These great ribs rest upon steel pins of 18 inches diameter, placed at the springing of the arch. The arches rise from massive masonry piers, which extend up to the level of the floor of the bridge. This floor is supported by vertical posts from the arches and is a little above the highest point of the rib. It is 152 feet above the surface of the river--having an elevation fifty feet greater than the well-known High Bridge, which spans the same valley within a quarter of a mile. The approaches to these steel arches on each side are granite viaducts carried over a series of stone arches. The whole structure forms a notable example of engineering construction. It was finished within two years from the beginning of work upon its foundations, the energy of its builders being worthy of special commendation.

* * * * *

In providing for the rapid transit of passengers in great cities the two types of construction successfully adopted are represented by the New York Elevated and the London Underground railways. The New York Elevated is a continuous metal viaduct, supported on columns varying in height so as to secure easy grades. The details of construction differ greatly at various parts of the elevated lines, those more recently built being able to carry much heavier trains than the earlier portions. The roads have been very successful in providing the facilities for transit so absolutely necessary in New York. The citizens of that city are alive to the present necessity of adding very soon to those facilities, and it is now only a question of the best method to be adopted to secure the largest results in a permanent manner.

The London Underground road has also been very successful. Its construction was a formidable undertaking. Its tunnels are not only under streets but under heavy buildings. Its daily traffic is enormous. The difficult question in its management is, as in all long tunnels, that of ventilation, but modern science will surely solve that, as it does so many other problems connected with the active life of man.

* * * * *

Many broad questions of general policy, and innumerable matters of detail are involved in the development of railway engineering. In the determination, for instance, of the location, the relations of cost and construction to future business, the possibilities of extensions and connections, the best points for settlements and industrial enterprises, the merits and defects of alternative routes must be weighed and decided.

Where structures are to be built, the amount and delicacy of detail requisite in their design and execution can hardly be described. Final pressures upon foundations must be ascertained and provided for. Accurate calculations of strains and stresses, involving the application of difficult processes and mechanical theories, must be made. The adjustment of every part must be secured with reference to its future duty. Strength and safety must be assured and economy not forgotten. Every contingency must, if possible, be anticipated, while the emergencies which arise during every great construction demand constant watchfulness and prompt and accurate decision.

The financial success of the largest enterprises rests upon such practical application of theory and experience. Even more weighty still is the fact that the safety of thousands of human lives depends daily upon the permanency and stability of railway structures. Such are some of the deep responsibilities which are involved in the active work of the Civil Engineer.

FOOTNOTE:

[8] Reference is made to the substitution of locks in the Panama Canal for the original project of a canal at the sea-level.

AMERICAN LOCOMOTIVES AND CARS.

BY M. N. FORNEY.

The Baltimore and Ohio Railroad in 1830--Evolution of the Car
from the Conestoga Wagon--Horatio Allen's Trial Trip--The
First Locomotive used in the United States--Peter Cooper's
Race with a Gray Horse--The "De Witt Clinton," "Planet," and
other Early Types of Locomotives--Equalizing Levers--How Steam
is Made and Controlled--The Boiler, Cylinder, Injector, and
Valve Gear--Regulation of the Capacity of a Locomotive to
Draw--Increase in the Number of Driving Wheels--Modern Types of
Locomotives--Variation in the Rate of Speed--The Appliances by
which an Engine is Governed--Round-houses and Shops--Development
of American Cars--An Illustration from Peter Parley--The Survival
of Stage Coach Bodies--Adoption of the Rectangular Shape--The
Origin of Eight-wheeled Cars--Improvement in Car Coupling--A
Uniform Type Recommended--The Making of Wheels--Relative Merits
of Cast and Wrought Iron, and Steel--The Allen Paper Wheel--Types
of Cars, with Size, Weight, and Price--The Car-Builder's
Dictionary--Statistical.

Among the readers of this volume there will be some who have reached the summit of the "divide" which separates the spring and summer of life from its autumn and winter, and whose first information about railroads was received from Peter Parley's "First Book of History," which was used as a schoolbook forty or fifty years ago. In his chapter on Maryland, he says:

But the most curious thing at Baltimore is the railroad. I must
tell you that there is a great trade between Baltimore and the
States west of the Alleghany Mountains. The western people buy a
great many goods at Baltimore, and send in return a great deal of
western produce. There is, therefore, a vast deal of travelling
back and forth, and hundreds of teams are constantly occupied in
transporting goods and produce to and from market.[9]

Now, in order to carry on all this business more easily, the
people are building what is called a railroad. This consists of
iron bars laid along the ground, and made fast, so that carriages
with small wheels may run along upon them with facility. In this
way, one horse will be able to draw as much as ten horses on a
common road. A part of this railroad is already done, and if you
choose to take a ride upon it, you can do so. You will mount a
car something like a stage, and then you will be drawn along by
two horses, at the rate of twelve miles an hour.

The picture reproduced below (Fig. 2) of a car drawn by horses was given with the above description of the Baltimore & Ohio Railroad. The mutilated copy of the book from which the engraving and extract were copied does not give the date when it was written or published. It was probably some time between the years 1830 and 1835. That the car shown in the engraving was evolved from the Conestoga wagon is obvious from the illustrations.

This engraving and description, made for children, more than fifty years ago, will give some idea of the state of the art of railroading at that time; and it is a remarkable fact that the present wonderful development and the improvements in railroads and their equipments in this country have been made during the lives of persons still living.

In the latter part of 1827, the Delaware & Hudson Canal Company put the Carbondale Railroad under construction. The road extends from the head of the Delaware & Hudson Canal at Honesdale, Pa., to the coal mines belonging to the Delaware & Hudson Canal Company at Carbondale, a distance of about sixteen miles. This line was opened, probably in 1829, and was operated partly by stationary engines, and partly by horses. The road is noted chiefly for being the one on which a locomotive was first used in this country. This was the "Stourbridge Lion," which was built in England under the direction of Mr. Horatio Allen, who afterward was president of the Novelty Works in New York, and who is still (1889) living near New York at the ripe age of eighty-seven. Before the road was opened, he had been a civil engineer on the Carbondale line. In 1828 Mr. Allen went to England, the only place where a locomotive was then in daily operation, to study the subject in all its practical details. Before leaving this country he was intrusted by the Delaware & Hudson Canal Company with the commission to have rails made for that line, and to have three locomotives built on plans to be decided by him when in England. This, it must be remembered, was before the celebrated trial of the "Rocket" on the Liverpool & Manchester Railway, which was not made until 1829. Previous to that trial, it had not been decided what type of boiler was the best for locomotives. The result of Mr. Allen's investigations was to produce in his mind a decided confidence in the multitubular boiler which is now universally used for locomotives. Other persons of experience recommended a boiler with small riveted flues of as small diameter as could be riveted. An order was therefore given to Messrs. Foster, Rastrick & Co., at Stourbridge, for one engine whose boiler was to have riveted flues of comparatively large size, and another order was given to Messrs. Stephenson & Co., of Newcastle-on-Tyne, for two locomotives with boilers having small tubes. The engine built by Foster, Rastrick & Co. was named the "Stourbridge Lion." It was sent to this country and was tried at Honesdale, Pa., on August 9, 1829. On its trial trip it was managed by Mr. Allen, to whom belongs the distinction of having run the first locomotive that was ever used in this country. In 1884 he wrote the following account of this trip:

When the time came, and the steam was of the right pressure,
and all was ready, I took my position on the platform of the
locomotive alone, and with my hand on the throttle-valve handle
said: "If there is any danger in this ride it is not necessary
that the life and limbs of more than one should be subjected to
that danger."

The locomotive, having no train behind it, answered at once to
the movement of the hand; ... soon the straight line was run
over, the curve was reached and passed before there was time
to think as to its not being passed safely, and soon I was
out of sight in the three miles' ride alone in the woods of
Pennsylvania. I had never run a locomotive nor any other engine
before; I have never run one since.

The two engines contracted for with Messrs. Stephenson & Co. were made by them, and Mr. Allen has informed the writer that they were built on substantially the same plans that were afterward embodied in the famous "Rocket." They were shipped to New York and for a time were stored in an iron warehouse on the east side of the city, where they were exhibited to the public. They were never sent to the Delaware & Hudson Canal Company's road, and it is not now known whatever became of them. If they had been put to work on their arrival here the use of engines of the "Rocket" type would have been anticipated on this side the Atlantic.

The first railroad which was undertaken for the transportation of freight and passengers in this country, on a comprehensive scale, was the Baltimore & Ohio. Its construction was begun in 1828. The laying of rails was commenced in 1829, and in May, 1830, the first section of fifteen miles from Baltimore to Ellicott's Mills was opened. It was probably about this time that the animated sketch of the car given by Peter Parley was made. From 1830 to 1835 many lines were projected, and at the end of that year there were over a thousand miles of road in use.

Whether the motive power on these roads should be horses or steam was for a long time an open question. The celebrated trial of locomotives on the Liverpool & Manchester Railway, in England, was made in 1829. Reports of these trials, and of the use of locomotive engines on the Stockton & Darlington line, were published in this country, and, as Mr. Charles Francis Adams says, "The country, therefore, was not only ripe to accept the results of the Rainhill contest, but it was anticipating them with eager hope." In 1829 Mr. Horatio Allen, who had been in England the year before to learn all that could then be learned about steam locomotion, reported to the South Carolina Railway Company in favor of steam instead of horse power for that line. The basis of that report, he says, "Was on the broad ground that in the future there was no reason to expect any material improvement in the breed of horses, while, in my judgment, the man was not living who knew what the breed of locomotives was to place at command."

As early as 1829 and 1830, Peter Cooper experimented with a little locomotive on the Baltimore & Ohio Railroad (Fig. 4). At a meeting of the Master Mechanics' Association in New York, in 1875--at the Institute which bears his name--he related with great glee how on the trial trip he had beaten a gray horse, attached to another car. The coincidence that one of Peter Parley's horses is a gray one might lead to the inference that it was the same horse that Peter Cooper beat, a deduction which perhaps has as sound a basis to rest on as many historical conclusions of more importance.

The undeveloped condition of the art of machine construction at that time is indicated by the fact that the flues of the boiler of this engine were made of gun-barrels, which were the only tubes that could then be obtained for the purpose. The boiler itself is described as about the size of a flour-barrel. The whole machine was no larger than a hand-car of the present day.

In the same year that Peter Cooper built his engine, the South Carolina Railway Company had a locomotive, called the "Best Friend," built at the West Point Foundry for its line. In 1831 this company had another engine, the "South Carolina" (Fig. 5), which was designed by Mr. Horatio Allen, built at the same shop. It was remarkable in having eight wheels, which were arranged in two trucks. One pair of driving-wheels, _D D_ and _D′ D′_, and a pair of leading-wheels, _L L_ and _L′ L′_, were attached to frames, _c d e f_ and _g h i j_, which were connected to the boiler by kingbolts, _K K′_, about which the trucks could turn. Each pair of driving-wheels had one cylinder, _C C′_. These were in the middle of the engine and were connected to cranks on the axles _A_ and _B_.

The "De Witt Clinton" (Fig. 6) was built for the Mohawk & Hudson Railroad, and was the third locomotive made by the West Point Foundry Association. The first excursion trip was made with passengers from Albany to Schenectady, August 9, 1831. This is the engine shown in the silhouette engraving of the "first[10] railroad train in America" which in recent years has been so widely distributed as an advertisement.

In 1831 the Baltimore & Ohio Railroad Company offered a premium of $4,000 "for the most approved engine which shall be delivered for trial upon the road on or before the 1st of June, 1831; and $3,500 for the engine which shall be adjudged the next best." The requirements were as follows:

The engine, when in operation, must not exceed three and one-half
tons weight, and must, on a level road, be capable of drawing day
by day fifteen tons, inclusive of the weight of wagons, fifteen
miles per hour.

In pursuance of this call upon American genius, three locomotives were produced, but only one of these was made to answer any useful purpose. This engine, the "York," was built at York, Pa., and was brought to Baltimore over the turnpike on wagons. It was built by Davis & Gartner, and was designed by Phineas Davis, of that firm, whose trade and business was that of a watch and clock maker. After undergoing certain modifications, it was found capable of performing what was required by the company. After thoroughly testing this engine, Mr. Davis built others, which were the progenitors of the "grasshopper" engines (Fig. 7) which were used for so many years on the Baltimore & Ohio Railroad. It is a remarkable fact that three of these are still in use on that road, and have been in continuous service for over fifty years. Probably there is no locomotive in existence which has had so long an _active_ life.

In August, 1831, the locomotive "John Bull," which was built by George & Robert Stephenson & Company, of Newcastle-upon-Tyne, was received in Philadelphia, for the Camden & Amboy Railroad & Transportation Company. This is the old engine which was exhibited by the Pennsylvania Railroad Company at the Centennial Exhibition in 1876. After the arrival of the "John Bull" a very considerable number of locomotives which were built by the Stephensons were imported from England. Most of them were probably of what was known as the "Planet" class (Fig. 8), which was a form of engine that succeeded the famous "Rocket."

The following quotation is from "The Early History of Locomotives in this Country," issued by the Rogers Locomotive & Machine Works:

These locomotives, which were imported from England, doubtless
to a very considerable extent, furnished the types and patterns
from which those which were afterward built here were fashioned.
But American designs very soon began to depart from their
British prototypes, and a process of adaptation to the existing
conditions of the railroads in this country followed, which
afterward "differentiated" the American locomotives more and more
from those built in Great Britain. A marked feature of difference
between American and English locomotives has been the use of a
"truck" under the former.

In all of the locomotives which have been illustrated, excepting the "South Carolina," the axles were held by the frames so that the former were always parallel to each other. In going around curves, therefore, there was somewhat the same difficulty that there would be in turning a corner with an ordinary wagon if both its axles were held parallel, and the front one could not turn on the kingbolt. The plan of the wheels and running gear of the "South Carolina" shows the position that they assumed on a curved track (Fig. 5). It will be seen that, by reason of their connection to the boiler by kingbolts, _K K′_, the two pairs of wheels could adjust themselves to the curvature of the rails. This principle was afterward applied to cars, and nearly all the rolling-stock in this country is now constructed on this plan, which was proposed by Mr. Allen in a report dated May 16, 1831, made to the South Carolina Canal & Railroad Company; and an engine constructed on this principle was completed the same year.

In the latter part of the year 1831 the late John B. Jervis invented what he called "a new plan of frame, with a bearing-carriage for a locomotive engine," for the use of the Mohawk & Hudson Railroad. Jervis's engine is shown by Figure 9. In a letter published in the _American Railroad Journal_ of July 27, 1833, he described the objects aimed at in the use of the truck as follows:

The leading objects I had in view, in the general arrangement
of the plan of the engine, did not contemplate any improvement
in the power over those heretofore constructed by Stephenson &
Company,[11] but to make an engine that would be better adapted
to railroads of less strength than are common in England; that
would travel with more ease to itself and to the rail on curved
roads; that would be less affected by inequalities of the rail,
than is attained by the arrangement in the most approved engines.

In Jervis's locomotive the main driving-axle, _A_, shown in the plan of the wheels and running gear, was rigidly attached to the engine-frame, _a b c d_, and only one truck, or "bearing-carriage," _e f g h_, consisting of the two pairs of small wheels attached to a frame, was used. This was connected to the main engine-frame by a kingbolt, _K_, as in Allen's engine.

The position of its wheels on a curve, and the capacity of the truck, or "bearing-carriage," to adapt itself to the sinuosities of the track are shown in the plan. The effectiveness of the single truck for locomotives, in accomplishing what Mr. Jervis intended it for, was at once recognized, and its almost general adoption on American locomotives followed.

In 1834, Ross Winans, of Baltimore, patented the application of the principle which Mr. Allen had proposed and adopted for locomotives "to passenger and other cars." He afterward brought a number of actions at law against railroads for infringement of his patent, which was a subject of legal controversy for twenty years. Winans claimed that his invention originated as far back as 1831, and was completed and reduced to practice in 1834. The dispute was finally carried to the Supreme Court of the United States, and was decided against the plaintiff, after an expenditure of as much as $200,000 by both sides. It involved the principle on which nearly all cars in this country are now and were then built; and, as one of the counsel for the defendants has said, "It was at one time a question of millions, to be assured by a verdict of a jury."

In 1836, Henry R. Campbell, of Philadelphia, patented the use of two pairs of driving-wheels and a truck, as shown in Figure 10. The driving-wheels were coupled by rods, as may be seen below. This plan has since been so generally adopted in this country that it is now known as the "American type" of locomotive, and is the one almost universally used here for passenger, and to a considerable extent for freight, service. An example of a modern locomotive of this type is represented by Figure 11.

From these comparatively small beginnings, the magnificent equipment of our railroads has grown. From Peter Cooper's locomotive, which weighed less than a ton, with a boiler the size of a flour-barrel, and which had difficulty in beating a gray horse, we now have locomotives which will easily run sixty and can exceed seventy miles an hour, and others which weigh seventy-five tons and over. A comparison of the engraving of Peter Cooper's engine with that of the modern standard express passenger locomotive (Fig. 11) shows vividly the progress which has been made since that first experiment was tried--little more than half a century ago. In that period there have been many modifications in the design of locomotives to adapt them to the changed conditions of the various kinds of traffic of to-day. An express train travelling at a high rate of speed requires a locomotive very different from one which is designed for handling heavy freight trains up steep mountain grades. A special class of engines is built for light trains making frequent stops, as on the elevated railroads in New York, and those provided for suburban traffic (Fig. 12)--and still others for street railroads (Fig. 13), for switching cars at stations (Fig. 14), etc. [Pp. 110 and 113]. The process of differentiation has gone on until there are now as many different kinds of these machines as there are breeds of dogs or horses.

Nearly all the early locomotives had only four wheels. In some cases one pair alone was used to drive the engine, and in others the two pairs were coupled together, so that the adhesion of all four could be utilized to draw loads. The four-wheeled type is still used a great deal for moving cars at stations, and other purposes where the speed is comparatively slow. But to run around sharp curves the wheels of such engines must be placed near together, just as they are under an ordinary street-car. This makes the wheel-base very short, and such engines are therefore very unsteady at high speeds, so that they are unsuited for any excepting slow service. They have the advantage, though, that the whole weight of the machine may be carried on the driving-wheels, and can thus be useful for increasing their friction, or adhesion to the rails. This gives such engines an advantage for starting and moving heavy trains, at stations or elsewhere, which is the kind of service in which they are usually employed.

If the front end of the engine is carried on a truck, as in Campbell's plan (Fig. 10)--which is the one that has been very generally adopted in this country--the wheel-base can be extended and at the same time the front wheels can adjust themselves to the curvature of the track. This gives the running-gear lateral flexibility. But as the tractive power of a locomotive is dependent upon the friction, or adhesion of the wheels to the rails, it is of the utmost importance that the pressure of the wheels on the rails should be uniform. For this reason the wheels must be able to adjust themselves to the vertical as well as the horizontal inequalities of the track.

Figure 15 shows the driving-wheels, axles, journal-boxes, and part of the frame and springs of an American type of engine--the circumference of the wheels only being shown. The axles _A A_ each have journal-boxes or bearings, _B B_, in which they turn. These boxes are held between the jaws _J J J J_ of the frames, and can slide vertically in the spaces _c c c c_ between the jaws. The frames are suspended on springs, _S S_, which bear on the boxes _B B_. The vertical motion of the boxes and the flexibility of the springs allow the wheels to adjust themselves to some extent to the unevenness of the track. But, in order to distribute the weight equally on the two wheels, the springs _S S_ on each side of the engine are connected together by an equalizing lever, _E E_. These levers each have a fulcrum, _F_, in the middle, and are connected by iron straps or hangers, _h h_, to the springs. It is evident that any strain or tension on one spring is transferred by the equalizing lever to the other spring, and thus the weight is equalized on both wheels.

But to give perfect vertical adjustment of such an engine to the track, still another provision must be made. Everyone has observed that a three-legged stool will always stand firm on any surface, no matter how irregular, but one with four legs will not. Now if the back end of a locomotive should rest on the fulcrums of the equalizing levers, as shown in Figure 15, and the front end should rest on the two sides of the truck, it would be in the condition of the four legged stool. Therefore, instead of resting on the two sides of the truck, locomotives are made to bear on the centre of it, so that they are carried on it and on the two fulcrums of the equalizing levers, which gives the machine the adjustability due to the three-legged principle. When more than four driving-wheels are used the springs are connected together by equalizing levers, as shown in Figure 29 (p. 124), which represents a consolidation engine as it appears before the wheels are put under it.

Having a vehicle which is adapted to running on a railroad track, it remains to supply the motive power. This, in all but some very few exceptional cases, is the expansive power of steam. What the infant electricity has in store for us it would be rash to predict, but for locomotives its steps have been thus far weak and uncertain, and when we want a giant of steel or a race-horse of iron our only sure reliance is steam. This is the breath of life to the locomotive, which is inhaled and exhaled to and from the cylinders, which act as lungs, while the boiler fulfils functions analogous to the digestive organs of an animal. A locomotive is as dependent on the action of its boiler for its capacity for doing work as a human being on that of his stomach. The mechanical appliances of the one and the mental and physical equipment of the other are nugatory without a good digestive apparatus.

Fig. 17.--Transverse Section.]

A locomotive boiler consists of a rectangular fireplace or fire-box, as shown at _A_, in Figure 16, which is a longitudinal section, and Figure 17 a transverse section through the fire-box. The fire-box is connected with the smoke-box _B_ by a large number of small tubes, _a a_, through which the smoke and products of combustion pass from the fire-box to the smoke-box, and from the latter they escape up the chimney _D_. The fire-box and tubes are all surrounded with water, so that as much surface as possible is exposed to the action of the fire. This is essential on account of the large amount of water which must be evaporated in such boilers. To create a strong draught, the steam which is exhausted from the cylinders is discharged up the chimney through pipes, and escapes at _e_. This produces a partial vacuum in the smoke-box, which causes a current of air to flow through the fire on the grate, into the fire-box, through the tubes, and thence to the smoke-box and up the chimney. Probably many readers have noticed, that of late years the smoke-boxes of locomotives have been extended forward in front of the chimneys. This has been done to give room for deflectors and wire netting inside to arrest sparks and cinders, which are collected in the extended front and are removed by a door or spout, _L_, below.

To get the water into the boiler against the pressure of steam a very curious instrument, called an injector, has been devised. Formerly force-pumps were used, but these are now being abandoned. The illustration (Fig. 18) shows what may be called a rudimentary injector. _B_ is a boiler and _E_ a conical tube open at its lower end--and connected to a water-supply tank by a pipe, _C_. A pipe, _A_, is connected with the steam-space of the boiler and terminates in a contracted mouth, _F_, inside of the cone _E_. If steam is admitted to _A_, it flows through the pipe and escapes at _F_. In doing so it produces a partial vacuum in _E_, and water is consequently drawn up the pipe _C_ from the tank. The current of steam now carries with it the water, and they escape at _G_. After flowing for a few seconds the water has a high velocity and the steam, mingling with the water, is condensed. The momentum of the water soon becomes sufficient to force the valve _H_ down against the pressure below it, and the jet of water then flows continuously into the boiler. A very curious phenomenon of this somewhat mysterious instrument is that if steam of a low pressure is taken from one boiler it will force water into another against a higher pressure. Figure 19 is a section of an actual injector used on locomotives.

Having explained how the steam is generated, it remains to show how it propels a locomotive. It does this very much as a person on a bicycle propels it--that is, by means of two cranks the wheels are made to revolve, and the latter must then either slip or the vehicle will move. In a locomotive the driving-wheels are turned by means of two cylinders and pistons, which are connected by rods to the cranks attached to the driving-wheels or axles. These cranks are placed at right angles to each other, so that when one of them is at the "dead-point" the piston connected with the other can exert its maximum power to rotate the wheels. This enables the locomotive to start with the pistons in any position; whereas, if one cylinder only was used it would be impossible to turn the wheels if the crank should stop at one of its dead-points.

It will probably interest a good many readers to know how the steam gets into the cylinders and moves the pistons and then gets out again, and how a locomotive is made to run either backward or forward at pleasure.

Figure 20 (p. 118) shows a section of a cylinder, _A A′_, with the piston _B_ and piston rod _R_. The cylinder has two passages, _c c_ and _d d_, which connect its ends with a box, _U_, called a steam-chest, to which steam is admitted from the boiler by a pipe, _J_. The two passages _c_ and _d_ have another one, _g_, between them, which is connected with the chimney. These passages are covered by a slide-valve, _V_, which moves back and forth in the steam-chest, alternately uncovering the openings _c_ and _d_. When the valve is in the position shown in Figure 20, obviously steam can flow into the front end _A_ of the cylinder through the passage _c_, as indicated by the darts. The valve has a cavity, _H_, underneath it. When this cavity is over the passage _d_ and _g_, it is plain that the steam in the back end _A′_ of the cylinder can flow through _d_ and _g_ and then escape up the chimney. Under these circumstances the steam in the front end _A_ of the cylinder will force the piston _B_ to the back end. When it reaches the back end of the cylinder the valve is moved into the position shown in Figure 21, and steam can then enter _d_ and will fill the back end _A′_ while that in the front end escapes through _c_ and _g_. The piston is then forced to the front end by the pressure of the steam behind it. It will thus be seen that the steam enters and escapes to and from the cylinder through the same openings.

From what has been said it is obvious, too, that every time the piston moves from one end of the cylinder to the other the valve must also be moved back and forth in the steam-chest. This is done by what is called an eccentric.

An "eccentric" is a disk or wheel (Fig. 22) with a hole, _S_, the size of the axle of the locomotive to which it is attached. The centre _n_ of the outside periphery of the eccentric is some distance from _S_, the centre of the shaft. A metal ring, _K K_ (Fig. 23), made in two halves, embraces the eccentric, and the latter revolves inside of this ring. A rod, _L_, is attached to the strap, and is connected with the valve so that the motion of the eccentric is communicated to it. It is obvious that if the eccentric revolves it will impart a reciprocating motion to the rod _L_, which is communicated to the valve.

Fig. 23.--Eccentric and Strap.]