F a railway train could travel over a rainbow, it would hardly have been necessary to build a bridge over the Zambesi River at the Victoria Falls, for during seven months of the year a rainbow can always be seen there; but about the end of August the fairy architects take it down, and do not come to build it again until the beginning of February. The rainbow is made by the sunlight shining on the dancing drops of spray that leap from the waterfall while the river is in flood. But when, after the end of August, the flood subsides, the spray subsides too, and the lovely rainbow fades from sight until the rainy season has returned.

This mighty river collects its waters over a space of a million square miles, but on its way to the sea is met by many difficulties. The greatest of these occurs near Kazungula, on the borders of Rhodesia, and is known by the natives as the 'place of the sounding smoke.' David Livingstone, who, fifty years ago, was the first white man to see it, called it the Victoria Falls, and has told the world how he crept to the edge of the awful abyss and peered over in the vain effort to see the bottom through that roaring, blinding cloud of 'sounding smoke.' Long, long ages ago a terrible earthquake occurred at this spot, and from shore to shore of the Zambesi (which is here more than a mile wide) a huge crack, one hundred yards across, suddenly opened. Into this the river disappears with a mighty thunder, as though to lose itself in the centre of the earth. Four hundred feet down the bottom of the chasm is reached, and, beating themselves against the opposite wall, the waters struggle to find an outlet, throwing up in their fury white clouds of spray, which rise to a height of one thousand two hundred feet, and can be seen for a distance of ten miles.

Near the eastern end of the mile-long crack, there is an opening in the form of a narrow gorge one hundred yards wide, twisting and twining in the most erratic manner for more than twenty miles to the southward. And through this, imprisoned by rocky cliffs four hundred feet high, the boiling Zambesi struggles on its way to the sea. On the lip of the cataract, as though carried to the edge by the flowing waters, hang green wooded isles, glittering with the ever-falling spray and waving light fronds of fern and palm, in the cool airs that are constantly being driven by the falls from the depths below them. It is a spot of great beauty, and it is no wonder that many people expressed regret when they learned that the railway was fast approaching, and would leap across the gorge through which the waters escape. But after all, in a scene of such magnitude, we may hope that the railway will show no more than a scratch in the wide sea-sands.

The spot chosen for the bridge is some four hundred yards below the falls, and, owing to the sudden bends in the channel, the merest glimpse only can be caught of the falling water.

Sir Charles Metcalf, engineer of the Rhodesian Railway Company, having surveyed the place, made a design for the bridge, and a firm of engineers in Darlington, England, undertook to build it. In the meantime, the railway at Buluwayo, three hundred miles away, had been continued to the edge of the gorge in readiness to convey the material.

It was decided that the bridge should be in the form of an arch made of steel girders, the central span being five hundred feet. The work was begun in October, 1904. First a pair of 'shear legs' was erected on the southern side opposite the place where the railway from Buluwayo ended. This is a mechanical contrivance of the nature of a crane, capable of being raised and lowered, and is formed of two or more poles standing some yards apart at their feet, but joined together at their heads, to support a revolving pulley. To save the loss of time and great inconvenience of crossing the river above the falls, it became necessary to find some means of spanning this narrow gorge before beginning to build the bridge. This was accomplished by firing a sky-rocket from the northern cliff-top with a length of light string attached. To the end of the string a slightly stouter cord was tied; then a strong rope, and finally a wire cable two inches thick. Thus, that which could not be done all at once, was done by degrees. The wire cable, being passed over the pulley on the shear legs, was fastened on the other side of the gorge to the top of a steel tower, thirty-six feet high.

From this thin aerial railway hung the 'cage' in which the workmen would cross and recross, and do a great deal of the bridge-building work, being raised and lowered to the required position by the shear legs. Some feet above the two-inch rope ran an electric wire with a motor engine which propelled the car backwards and forwards. Thus we may almost say that the first conveyance across the Zambesi was an electric tram. And the passengers (particularly on the first journey) were not pleased with the trip. They shrank with pardonable terror when they found themselves suspended over that awful gulf by a slender cord that swayed against the sky. But use soon changed all this.

The bridge was begun from both sides at once. In the rocky sides of the cliffs excavations were made to receive the four upright columns from which the arch would spring. On beds of concrete poured into these excavations was bolted an iron plate upon which the foot of the 'post' would hinge, so as to allow movement when the iron girders expanded or contracted with the change of temperature. The 'posts' are one hundred and five feet tall, and the arch which springs from their feet rises to a height of ninety feet at the centre. As the two ends grew towards each other across the abyss, it was found that the weight would require support before the girders met in the middle. To build a scaffolding would of course have been impossible; so the following means were adopted. Into the rocky ground on both sides of the river, two holes were bored, each thirty feet deep and thirty feet apart, their bottom ends being connected by another boring. A strong wire rope was then threaded down one hole and up through the other, to be carried over the cliff-top and passed under the bridge-end as it hung in mid-air. As the weight increased the ropes were added to, while, as a further precaution, the ground between the two holes was loaded with five thousand tons of railway irons. The wire ropes successfully played their parts until April 1st, 1905, but when the central girder was ready to take its place, it was found to be an inch and a quarter too long. It had expanded in the heat; but after a night's cooling it contracted to the right size, and was successfully inserted.

One of the principal difficulties in the erection of this bridge has been the trouble of getting the material to the spot. From Darlington to the Victoria Falls is eight thousand miles of ocean, bush, and desert, and sometimes long delay was caused by the railway being washed away by floods. But once there was interruption from another cause. Many of the English workmen were unable to stop on account of the climate, and they were constantly drenched by the spray, until in many cases natives had to be employed in their stead. These natives were housed in a little settlement of nicely built huts, lighted by electricity. One day, however, the electric wires caused a fire which destroyed the entire 'town' with astonishing rapidity.

The bridge was opened in August, 1905, on the occasion of the visit of the British Association. The roadway over it is thirty feet wide, affording room for a double set of rails, and the panting trains have already begun to cross its web-like span, gliding into sight from the cliff-top on one side, only to disappear the next moment on the other in a green wilderness of ferns and tropic flowers.