Stories of Inventors Part 6

During the Boer War in South Africa two operators for the Biograph Company took their bulky machine (it weighed about eighteen hundred pounds) to the very firing-line and took pictures of battles between the British and the Burghers when they were exposed to the fire of both armies. On one occasion, in fact, the operator who was turning the mechanism--he sat on a bicycle frame, the sprocket of which was connected by a chain with the interior machinery--during a battle, was knocked from his place by the concussion of a sh.e.l.l that exploded nearby; nevertheless, the film was saved, and the same man rode on horseback nearly seventy-five miles across country to the nearest railroad point so that the precious photographic record might be sent to London and shown to waiting audiences there.

Pictures were taken by the kinetoscope showing an ascent of Mount Blanc, the operator of the camera necessarily making the perilous journey also; different stages of the ascent were taken, some of them far above the clouds. For this series of pictures a film eight hundred feet long was required, and 12,800 odd exposures or negatives were made.

Successive pictures have been taken at intervals during an ocean voyage to show the life aboard ship, the swing of the great seas, and the rolling and pitching of the steamer. The heave and swing of the steamer and the mountainous waves have been so realistically shown on the screen in the theatre that some squeamish spectators have been made almost seasick. It might be comforting to those who were made unhappy by the sight of the heaving seas to know that the operator who took one series of sea pictures, when lashed with his machine in the lookout place on the foremast of the steamer, suffered terribly from seasickness, and would have been glad enough to set his foot on solid ground; nevertheless, he stuck to his post and completed the series.

[Ill.u.s.tration: DEVELOPING MOVING-PICTURE FILMS The films are wound on the great drums and run through the developer in the troughs as the drums are slowly revolved.]

It was a biograph operator that was engaged in taking pictures of a fire department rushing to a fire. Several pieces of apparatus had pa.s.sed--an engine, hook-and-ladder company, and the chief; the operator, with his (then) bulky apparatus, large camera, storage batteries, etc., stood right in the centre of the street, facing the stream of engines, hose-wagons, and fire-patrol men. In order to show the contrast, an old-time hand-pump engine, dragged by a dozen men and boys, came along at full speed down the street, and behind and to one side of them followed a two-horse hose-wagon, going like mad. The men running with the old-time engine, not realising how narrow the s.p.a.ce was and unaware of the plunging horses behind, pa.s.sed the biograph man on one side on the dead run. The driver of the rapidly approaching team saw that there was no room for him to pa.s.s on the other side of the camera man, and his horses were going too fast to stop in the s.p.a.ce that remained. He had but an instant to decide between the dozen men and their antiquated machine and the moving-picture outfit. He chose the latter, and, with a warning shout to the photographer, bore straight down on the camera, which continued to do its work faithfully, taking dozens of pictures a second, recording even the strained, anxious expression on the face of the driver. The pole of the hose-wagon struck the camera-box squarely and knocked it into fragments, and the wheels pa.s.sed quickly over the pieces, the photographer meanwhile escaping somehow. By some lucky chance the box holding the coiled exposed film came through the wreck unscathed.

When that series was shown on the screen in a theatre the audience saw the engine and hook-and-ladder in turn come nearer and nearer and then rush by, then the line of running men with the old engine, and then--and their flesh crept when they saw it--a team of plunging horses coming straight toward them at frightful speed. The driver's face could be seen between the horses' heads, distorted with effort and fear. Straight on the horses came, their nostrils distended, their great muscles straining, their fore hoofs striking out almost, it seemed, in the faces of the people in the front row of seats. People shrank back, some women shrieked, and when the plunging horses seemed almost on them, at the very climax of excitement, the screen was darkened and the picture blotted out. The camera taking the pictures had continued to work to the very instant it was struck and hurled to destruction.

In addition to the stereopticon and its attendant mechanism, which is only suitable when the pictures are to be shown to an audience, a machine has been invented for the use of an individual or a small group of people. In the mutoscope the positives or prints are made on long strips of heavy bromide paper, instead of films, and are generally enlarged; the strip is cut up after development and mounted on a cylinder, so they radiate like the spokes of a wheel, and are set in the same consecutive order in which they were taken. The thousands of cards bearing the pictures at the outer ends are placed in a box, so that when the wheel of pictures is turned, by means of a crank attached to the axle, a projection holds each card in turn before the lens through which the observer looks. The projection in the top of the box acts like the thumb turning the pages of a book. Each of the pictures is presented in such rapid succession that the object appears to move, just as the scenes thrown on the screen by a lantern show action.

The mutoscope widens the use of motion-photography infinitely. The United States Government will use it to ill.u.s.trate the workings of many of its departments at the World's Fair at St. Louis: the life aboard war-ships, the handling of big guns, army maneuvers, the life-saving service, post-office workings, and, in fact, many branches of the government service will be explained pictorially by this means.

Agents for manufacturers of large machinery will be able to show to prospective purchasers pictures of their machines in actual operation.

Living, moving portraits have been taken, and by means of a hand machine can be as easily examined as pictures through a stereoscope. It is quite within the bounds of possibility that circulating libraries of moving pictures will be established, and that every public school will have a projecting apparatus for the use of films, and a stereopticon or a mutoscope. In fact, a sort of circulating library already exists, films or mutoscope pictures being rented for a reasonable sum; and thus many of the most important of the world's happenings may be seen as they actually occurred.

Future generations will have histories ill.u.s.trated with vivid motion pictures, as all the great events of the day, processions, celebrations, battles, great contests on sea and land are now recorded by the all-seeing eye of the motion-photographer's camera.

BRIDGE BUILDERS AND SOME OF THEIR ACHIEVEMENTS

In the old days when Rome was supreme a Caesar decreed that a bridge should be built to carry a military road across a valley, or ordered that great stone arches should be raised to conduct a stream of water to a city; and after great toil, and at the cost of the lives of unnumbered labourers, the work was done--so well done, in fact, that much of it is still standing, and some is still doing service.

In much the same regal way the managers of a railroad order a steel bridge flung across a chasm in the midst of a wilderness far from civilisation, or command that a new structure shall be subst.i.tuted for an old one without disturbing traffic; and, lo and behold, it is done in a surprisingly short time. But the new bridges, in contrast to the old ones, are as spider webs compared to the overarching branches of a great tree. The old type, built of solid masonry, is ma.s.sive, ponderous, while the new, slender, graceful, is built of steel.

One day a bridge-building company in Pennsylvania received the specifications giving the dimensions and particulars of a bridge that an English railway company wished to build in far-off Burma, above a great gorge more than eight hundred feet deep and about a half-mile wide. From the meagre description of the conditions and requirements, and from the measurements furnished by the railroad, the engineers of the American bridge company created a viaduct. Just as an author creates a story or a painter a picture, so these engineers built a bridge on paper, except that the work of the engineers' imagination had to be figured out mathematically, proved, and reproved. Not only was the soaring structure created out of bare facts and dry statistics, but the thickness of every bolt and the strain to be borne by every rod were predetermined accurately.

And when the plans of the great viaduct were completed the engineers knew the cost of every part, and felt so sure that the actual bridge in far-off Burma could be built for the estimated amount, that they put in a bid for the work that proved to be far below the price asked by English builders.

And so this company whose works are in Pennsylvania was awarded the contract for the Gokteik viaduct in Burma, half-way round the world from the factory.

[Ill.u.s.tration: BUILDING AN AMERICAN BRIDGE IN BURMAH This structure stretches 820 feet above the bottom of the Gokteik Gorge.

The viaduct was built entirely from above, as shown in this picture.]

In the midst of a wilderness, among an ancient people whose language and habits were utterly strange to most Americans, in a tropical country where modern machinery and appliances were practically unknown, a small band of men from the young republic contracted to build the greatest viaduct the world had ever seen. All the material, all the tools and machinery, were to be carried to the opposite side of the earth and dumped on the edge of the chasm. From the heaps of metal the small band of American workmen and engineers, aided by the native labourers, were to build the actual structure, strong and enduring, that was conceived by the engineers and reduced to working-plans in far-off Pennsylvania.

From ore dug out of the Pennsylvania mountains the steel was made and, piece by piece, the parts were rolled, riveted, or welded together so that every section was exactly according to the measurements laid out on the plan. As each part was finished it was marked to correspond with the plan and also to show its relation to its neighbour. It was like a gigantic puzzle. The parts were made to fit each other accurately, so that when the workmen in Burma came to put them together the tangle of beams and rods, of trusses and braces should be a.s.sembled into a perfect, orderly structure--each part in its place and each doing its share of the work.

With men trained to work with ropes and tackle collected from an Indian seaport, and native riveters gathered from another place, Mr. J.C. Turk, the engineer in charge, set to work with the American bridgemen and the constructing engineer to build a bridge out of the pieces of steel that lay in heaps along the brink of the gorge. First, the traveller, or derrick, shipped from America in sections, was put together, and its long arm extended from the end of the tracks on which it ran over the abyss.

From above the great steel beams were lowered to the masonry foundations of the first tower and securely bolted to them, and so, piece by piece, the steel girders were suspended in s.p.a.ce and swung this way and that until each was exactly in its proper position and then riveted permanently. The great valley resounded with the blows of hammers on red-hot metal, and the clangour of steel on steel broke the silence of the tropic wilderness. The towers rose up higher and higher, until the tops were level with the rim of the valley, and as they were completed the horizontal girders were built on them, the rails laid, and the traveller pushed forward until its arm swung over the foundation of the next tower.

And so over the deep valley the slender structure gradually won its way, supporting itself on its own web as it crawled along like a spider.

Indeed, so tall were its towers and so slender its steel cords and beams that from below it appeared as fragile as a spider's web, and the men, poised on the end of swinging beams or standing on narrow platforms hundreds of feet in air, looked not unlike the flies caught in the web.

The towers, however, were designed to sustain a heavy train and locomotive and to withstand the terrific wind of the monsoon. The pressure of such a wind on a 320-foot tower is tremendous. The bridge was completed within the specified time and bore without flinching all the severe tests to which it was put. Heavy trains--much heavier than would ordinarily be run over the viaduct--steamed slowly across the great steel trestle while the railroad engineers examined with utmost care every section that would be likely to show weakness. But the designers had planned well, the steel-workers had done their full duty, and the American bridgemen had seen to it that every rivet was properly headed and every bolt screwed tight--and no fault could be found.

The bridge engineer's work is very diversified, since no two bridges are alike. At one time he might be ordered to span a stream in the midst of a populous country where every aid is at hand, and his next commission might be the building of a difficult bridge in a foreign wilderness far beyond the edge of civilisation.

Bridge-building is really divided into four parts, and each part requires a different kind of knowledge and experience.

First, the designer has to have the imagination to see the bridge as it will be when it is completed, and then he must be able to lay it out on paper section by section, estimating the size of the parts necessary for the stress they will have to bear, the weight of the load they will have to carry, the effect of the wind, the contraction and expansion of cold and heat, and vibration; all these things must be thought of and considered in planning every part and determining the size of each. Also he must know what kind of material to use that is best fitted to stand each strain, whether to use steel that is rigid or that which is so flexible that it can be tied in a knot. On the designer depends the price asked for the work, and so it is his business to invent, for each bridge is a separate problem in invention, a bridge that will carry the required weight with the least expenditure of material and labour and at the same time be strong enough to carry very much greater loads than it is ever likely to be called upon to sustain. The designer is often the constructor as well, and he is always a man of great practical experience. He has in his time stepped out on a foot-wide girder over a rushing stream, directing his men, and he has floundered in the mud of a river bottom in a caisson far below the surface of the stream, while the compressed air kept the ooze from flowing in and drowning him and his workmen.

The second operation of making the pieces that go into the structure is simply the following out of the clearly drawn plans furnished by the designing engineers. Different grades of steel and iron are moulded or forged into shape and riveted together, each part being made the exact size and shape required, even the position of the holes through which the bolts or rivets are to go that are to secure it to the neighbouring section being marked on the plan.

The foundations for bridges are not always put down by the builders of the bridge proper; that is a work by itself and requires special experience. On the strength and permanency of the foundation depends the life of the bridge. While the foundries and steel mills are making the metal-work the foundations are being laid. If the bridge is to cross a valley, or carry the roadway on the level across a depression, the placing of the foundations is a simple matter of digging or blasting out a big hole and laying courses of masonry; but if a pier is to be built in water, or the land on which the towers are to stand is unstable, then the problem is much more difficult.

For bridges like those that connect New York and Brooklyn, the towers of which rest on bed-rock below the river's bottom, caissons are sunk and the ma.s.sive masonry is built upon them. If you take a gla.s.s and sink it in water, bottom up, carefully, so that the air will not escape, it will be noticed that the water enters the gla.s.s but a little way: the air prevents the water from filling the gla.s.s. The caisson works on the same principle, except that the air in the great boxlike chamber is highly compressed by powerful pumps and keeps the water and river ooze out altogether.

The caissons of the third bridge across the East River were as big as a good-sized house--about one hundred feet long and eighty feet wide. It took five large tugs more than two days to get one of them in its proper place. Anch.o.r.ed in its exact position, it was slowly sunk by building the masonry of the tower upon it, and when the lower edges of the great box rested on the bottom of the river men were sent down through an air-lock which worked a good deal like the lock of a ca.n.a.l. The men, two or three at a time, entered a small round chamber built of steel which was fitted with two air-tight doors at the top and bottom; when they were inside the air-lock, the upper door was closed and clamped tight, just as the gates leading from the lower level of a ca.n.a.l are closed after the boat is in the lock; then very gradually the air in the compartment is compressed by an air-compressor until the pressure in the air-lock is the same as that in the caisson chamber, when the lower door opened and allowed the men to enter the great dim room. Imagine a room eighty by one hundred feet, low and criss-crossed by ma.s.sive timber braces, resting on the black, slimy mud of the river bottom; electric lights shine dimly, showing the half-naked workmen toiling with tremendous energy by reason of the extra quant.i.ty of oxygen in the compressed air. The workmen dug the earth and mud from under the iron-shod edges of the caisson, and the weight of the masonry being continually added to above sunk the great box lower and lower. From time to time the earth was mixed with water and sucked to the surface by a great pump. With hundreds of tons of masonry above, and the watery mud of the river on all sides far below the keels of the vessels that pa.s.sed to and fro all about, the men worked under a pressure that was two or three times as great as the fifteen pounds to the square inch that every one is accustomed to above ground. If the pressure relaxed for a moment the lives of the men would be snuffed out instantly--drowned by the inrushing waters; if the excavation was not even all around, the balance of the top-heavy structure would be lost, the men killed, and the work destroyed entirely. But so carefully is this sort of work done that such an accident rarely occurs, and the caissons are sunk till they rest on bed-rock or permanent, solid ground, far below the scouring effect of currents and tides. Then the air-chamber is filled with concrete and left to support the great towers that pierce the sky above the waters.

[Ill.u.s.tration: THE SPIDER-WEB-LIKE VIADUCT ACROSS CANON DIABLO The slender steel structure supporting a loaded train that stretches along its entire length.]

The pneumatic tube, which is practically a steel caisson on a small scale operated in the same way, is often used for small towers, and many of the steel sky-sc.r.a.pers of the cities are built on foundations of this sort when the ground is unstable.

Foundations of wooden and iron piles, driven deep in the ground below the river bottom, are perhaps the most common in use. The piles are sawed off below the surface of the water and a platform built upon them, which in turn serves as the foundation for the masonry.

The great Eads Bridge, which was built across the Mississippi at St.

Louis, is supported by towers the foundations of which are sunk 107 feet below the ordinary level of the water; at this depth the men working in the caissons were subjected to a pressure of nearly fifty pounds to the square inch, almost equal to that used to run some steam-engines.

The bridge across the Hudson at Poughkeepsie was built on a crib or caisson open at the top and sunk by means of a dredge operated from above taking out the material from the inside. The wonder of this is hard to realise unless it is remembered that the steel hands of the dredge were worked entirely from above, and the steel rope sinews reached down below the surface more than one hundred feet sometimes; yet so cleverly was the work managed that the excavation was perfect all around, and the crib sank absolutely straight and square.

It is the fourth department of bridge-building that requires the greatest amount not only of knowledge but of resourcefulness. In the final process of erection conditions are likely to arise that were not considered when the plans were drawn.

The chief engineer in charge of the erection of a bridge far from civilisation is a little king, for it is necessary for him to have the power of an absolute monarch over his army of workmen, which is often composed of many different races.

With so many thousand tons of steel and stone dumped on the ground at the bridge site, with a small force of expert workmen and a greater number of unskilled labourers, in spite of bad weather, floods, or fearful heat, the constructing engineer is expected to finish the work within the specified time, and yet it must withstand the most exacting tests.

In the heart of Africa, five hundred miles from the coast and the source of supplies, an American engineer, aided by twenty-one American bridgemen, built twenty-seven viaducts from 128 to 888 feet long within a year.

The work was done in half the time and at half the cost demanded by the English bidders. Mr. Lueder, the chief engineer, tells, in his account of the work, of shooting lions from the car windows of the temporary railroad, and of seeing ostriches try to keep pace with the locomotive, but he said little of his difficulties with unskilled workmen, foreign customs, and almost unspeakable languages. The bridge engineer the world over is a man who accomplishes things, and who, furthermore, talks little of his achievements.

Though the work of the bridge builders within easy reach of the steel mills and large cities is less unusual, it is none the less adventurous.

In 1897, a steel arch bridge was completed that was built around the old suspension bridge spanning the Niagara River over the Whirlpool Rapids.

The old suspension bridge had been in continuous service since 1855 and had outlived its usefulness. It was decided to build a new one on the same spot, and yet the traffic in the meantime must not be disturbed in the least. It would seem that this was impossible, but the engineers intrusted with the work undertook it with perfect confidence. To any one who has seen the rushing, roaring, foaming waters of unknown depth that race so fast from the spray-veiled falls that they are heaped up in the middle, the mere thought of men handling huge girders of steel above the torrent, and of standing on frail swinging platforms two hundred or more feet above the rapids, causes chills to run down the spine; yet the work was undertaken without the slightest doubt of its successful fulfilment.

It was manifestly impossible to support the new structure from below, and the old bridge was carrying about all it could stand, so it was necessary to build the new arch, without support from underneath, over the foaming water of the Niagara rapids two hundred feet below. Steel towers were built on either side of the gorge, and on them was laid the platform of the bridge from the towers nearest to the water around and under the old structure. The upper works were carried to the solid ground on a level with the rim of the gorge and there securely anch.o.r.ed with steel rods and chains held in masonry. Then from either side the arch was built plate by plate from above, the heavy sheets of steel being handled from a traveller or derrick that was pushed out farther and farther over the stream as fast as the upper platform was completed.

The great ma.s.s of metal on both sides of the Niagara hung over the stream, and was only held from toppling over by the rods and chains solidly anch.o.r.ed on sh.o.r.e. Gradually the two ends of the uncompleted arch approached each other, the amount of work on each part being exactly equal, until but a small s.p.a.ce was left between. The work was so carefully planned and exactly executed that the two completed halves of the arch did not meet, but when all was in readiness the chains on each side, bearing as they did the weight of more than 1,000,000 pounds, were lengthened just enough, and the two ends came together, clasping hands over the great gorge. Soon the tracks were laid, and the new bridge took up the work of the old, and then, piece by piece, the old suspension bridge, the first of its kind, was demolished and taken away.

Over the Niagara gorge also was built one of the first cantilever bridges ever constructed. To uphold it, two towers were built close to the water's edge on either side, and then from the towers to the sh.o.r.es, on a level with the upper plateau, the steel fabric, composed of slender rods and beams braced to stand the great weight it would have to carry, was built on false work and secured to solid anchorages on sh.o.r.e. Then on this, over tracks laid for the purpose, a crane was run (the same process being carried out on both sides of the river simultaneously), and so the span was built over the water 239 feet above the seething stream, the sh.o.r.e ends balancing the outer sections until the two arms met and were joined exactly in the middle. This bridge required but eight months to build, and was finished in 1883. From the car windows hardly any part of the slender structure can be seen, and the train seems to be held over the foaming torrent by some invisible support, yet hundreds of trains have pa.s.sed over it, the winds of many storms have torn at its members, heat and cold have tried by expansion and contraction to rend it apart, yet the bridge is as strong as ever.

Sometimes bridges are built a span or section at a time and placed on great barges, raised to just their proper height, and floated down to the piers and there secured.