Chatterbox.

MARVELS OF MAN'S MAKING.

I.—THE BROOKLYN SUSPENSION BRIDGE.

HEN two large cities stand opposite to one another on the banks of a river, it is not likely they can do very well without a bridge to connect them. Yet the citizens of New York and Brooklyn were obliged to manage as best they could for a good many years before they had their bridge. There were many difficulties in the way. For one thing, the river is very broad; for another, the tall-masted ships ply up and down so frequently that it would never do to build anything which would obstruct their passage; and to overcome these difficulties would mean the expenditure of a vast sum of money. But the folk who earned their daily bread in New York and lived in Brooklyn grew thoroughly tired of spending chilly hours in foggy weather on the river-side piers, waiting for the ferry-boat to come and take them across, and at last they began an agitation which resulted in the Brooklyn Bridge.

The engineer who made the first design was Mr. John A. Raebling; but he did not live to see it carried into effect; for one summer day in 1869, when selecting the spot at which the great work should be begun, he met with an accident which caused his death a few days later. His son, Mr. Washington Raebling, then took the lead. Plans were carefully drawn and submitted to the Government, who, after much consideration, ordered that the bridge should be five feet higher and five feet wider. This apparently slight change added about 172,800l. to the cost of building, for little changes in big things mean more than big changes in little ones. The original cost was to be 10,800,000 dollars, or about 2,160,000l.; but in the end it amounted to nearly 3,100,000l.

Before we talk of the trouble and labour, let us look for a moment at the great things the engineers have accomplished.

The Brooklyn bridge is five thousand eight hundred and eighty-nine feet long and eighty-five feet wide. The huge cables that support it stretch like the strands of a monster spider-web from the tops of two towers, each two hundred and seventy-six feet high and standing one thousand five hundred and ninety-five feet apart. The above is the length of the central span; the two other spans, from the land to the towers, are each nine hundred and thirty feet long in addition. The roadway, one hundred and thirty-five feet above the river, is divided into five parts. The two outside ones are for vehicles, the middle one for foot passengers, and the remaining two for cable trams. The footway is eight feet higher than the others, so that an uninterrupted view is gained from it. The four cables supporting this heavy structure are anchored at both ends in blocks of masonry weighing sixty thousand tons each; so that there is little fear of their being dragged from their moorings. The bridge was opened amid a blaze of fireworks on May 24th, 1883.

On May 7th, 1870, the tower on the riverside at Brooklyn was begun, and completed just five years later; its companion on the opposite side was a year behind it. The foundations of these great towers lie in solid rock seventy-eight feet below the high-tide line on the New York side, and only a little less on the Brooklyn side.

The towers once completed, the task of laying the cables across from summit to summit engaged the thoughts of the engineers. This was no ordinary case of swinging a steel rope across a river, for the gigantic size and weight of the cables made it impossible to use ordinary means. First of all it would be necessary to make a communication from tower to tower. To accomplish this, one end of a coiled steel rope was carried to the top of the Brooklyn tower and passed over until it dangled into the river beneath. Here a steamboat dragged it across the river to the foot of the New York tower, where it was hauled up, and having been passed over the top, was carried down to the masonry anchorage already mentioned. Here it was wound round a revolving drum or pulley, and started back again to Brooklyn in the same manner, thus forming an endless band along which material could be carried by revolving the pulley at either end.

Though this rope was three-quarters of an inch in thickness, it was almost invisible to the people on the river, two hundred and seventy-six feet below. Yet it was the first 'stitch' in the great web, and thousands of eyes were turned towards it on August 25th, 1876, when the very first passenger crossed along it from shore to shore. This passenger was Mr. Farrington, one of the engineers. He wished to encourage his men by a good example, for over that terrible gulf it would soon be necessary for many of them to go. His seat was a small piece of board such as we use for a swing in a playground, and it was attached to the wire by four short ropes. The perilous journey took more than twenty minutes, and the people below watched almost breathlessly as the slender thread swayed up and down with the weight of the traveller. To their eyes it appeared at times as if he was soaring through the air unsupported, so thin was the line by which he hung.

And now the weaving of the cables began, and this was perhaps the most remarkable undertaking in the construction of the great bridge. To the endless band by which Mr. Farrington had crossed, there was fixed what is called a 'carrier.' This was to grip the end of the first wire (as the eye of the needle takes the thread); bear it across the river over the tops of the lofty towers; 'stitch' it to the New York shore (or anchorage) and bring it back again.

And that is what it did. This new wire (only one-eight of an inch thick—thinner, that is, than the first wire, on which Mr. Farrington had crossed) was two hundred miles long, and it had to perform the journey many hundred times before the first 'skein' was complete. Thus you will see that a single 'skein' stretched from shore to shore, consisting of nearly three hundred separate threads. These were bound tightly together at frequent intervals, and when a bunch of nineteen of them had been made, the first cable was ready for completion. But this was a matter of great difficulty. You will easily understand that it was necessary for every wire to do its share in bearing the weight of the bridge. Therefore, they must all be at an equal strain from tower to tower. Now you know that on a sunny day a bar of steel is longer than it is on a cloudy day, for the metal expands with heat. Consequently, when the sun came out to see what they were doing at Brooklyn, the wires upon which it shone became longer than those in the shadow behind them. Of course, in a short distance this would not be noticeable, but it made such a difference in the work we are describing, that the strength of the cable would have been greatly lessened had the strands been bound together in the sunshine, while some of the wires were slack, and some were tight. Even the wind interfered sadly; but by choosing dull, still days, when all the wires were subjected to the same temperature, they were at last successfully bound together.

Notwithstanding the perilous nature of this cable-weaving, it was attended by only one serious accident, and that was when one of the 'skeins' broke loose from the New York shore, and, leaping like the lash of a giant whip over the tower top, plunged into the river below. It narrowly missed the ferry-boats and other craft.

The effect of the temperature on such vast quantities of metal is shown in many ways. By shortening and lengthening the cables, it heightens and lowers the bridge, which is consequently slightly higher above the river in winter than it is in summer. At the tower-tops the cables rest on huge iron saddles, which are placed upon forty steel rollers, so that the cables may move more freely in expanding and contracting. Again, the bridge itself is not made in one piece, but is severed half-way across and provided with a sliding joint, so that all shall act obediently to the dictates of the ever-changing weather.

Thus you see there is more in building a bridge than appears to those who do not remember that a knowledge of nature's laws must guide the architect's hand when he is drawing his plans, and govern the engineer's tools when he is carrying those plans into effect.

John Lea.

'You might do it for me, just this once, Barton,' said Lopes in a tone of anxiety not often heard from a schoolboy. 'Your father is a rich man, and you can always get all the money you want from him, and if you will only lend me this, I will never borrow from you again. Do ask for the money at once!'