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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 71428 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

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 recently built at Niagara, only a few rods from the suspension bridge and a short distance below the great falls. It is shown in the illustrations on pages 26 and 31. 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 16 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 [see p. 26]. 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 pinconnected 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 just built over the St. Lawrence near Montreal [p. 28] 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 proposed cantilever Forth Bridge, with its two spans of 1,710 feet each, is in steady progress of construction and will when pleted mark a long step in advance in the science of bridge construction.

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Of entirely different design and principle from all these trusses are the beautiful steel arches of the St. Louis Bridge [p. 27], 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 23 to 8 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 riverbed is deepened, sometimes with amazing rapidity. In winter the river is

Old Stone Towers of the Niagara Suspension Bridge.

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 to 2 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 twentythree 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 now in process of erection over the Harlem Valley in the city of New York [p. 18] 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.

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The New Iron Towers of the Same

These

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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 will form a notable example of engineering construction. It will be 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.

DEATH AND JUSTICE.

By Graham R. Tomson.

EATH doth not claim us with the passing breath;

D' Before our Lady Justice calm he stands

To hear her grave, immutable commands; "Wait, I shall tell you presently," she saith, "Wait but a moment's space, my brother, Death, While Time, our kinsman, shakes his silent sands." She holds the balance true, with steady hands And strong, the little while it wavereth.

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MAESTRO AMBROGIO.

By T. R. Sullivan.

IN a certain narrow street of Florence, near Andrea del Sarto's house and the Annunziata's choir, where with maimed rites the mortal part of the poor painter senza errore was hurried under the pavement, there lived in the latter half of the fifteenth century a learned doctor whose name and titles history is scarcely able to recall. Yet the young Andrea may have known him; and the illustrious Leonardo, called Da Vinci, wise in many things and ennobling all with a touch rarer than the golden one of fable, was surely numbered among his friends. But the doctor led a life of deep seclusion, indifferent to the storms of party strife, to plot and insurrection, battles and murders, the tyrant's yoke, the tyrant's favor. His four gray walls sheltered him from the summer's heat, the winter's cold; his little garden caught from the sunlight all the colors

of the prism in roses, wild pomegranates, and oleanders. The laboratory behind it held his store of manuscripts, his retorts and crucibles, his furnace and his bellows-all the apparatus needed for experiments which so absorbed him that he seldom went out into the bus

tling streets. He had but one thought, one purpose: to make some vast discovery which should benefit the human race; and as he was human, too, one may imagine that his ambition went a little farther, coupling with the glorious result his own name, and immortalizing that. Undoubtedly, he longed and hoped to live forever in men's hearts; to have his ashes consecrated in a gilded shrine, surmounted by a marble busta goal of pilgrimage. Alas! None knows where he lies buried. You may find his house to-day in the Via del Mandorlo; his laboratory has been turned into a stable; the roses still run riot in his garden, and the snails still nibble at their leaves; but the last of many tenants, treading the very paths he trod, will smile and tell you that the

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