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76 Will the two ends meet? The engineers are confident that they will. One important fact remains to be pointed out. The two sides have not advanced with equal rapidity. On the Italian side the summit is nearly gained—before these pages are published it will have been passed; but on the French side they are nearly 2000 yards short of it. The work is still to be carried on simultaneously, and, consequently, on the Italian side they will shortly begin to descend. M. Conte mentioned that one of the reasons which influenced the engineers to drive the tunnel to a summit, was, that by so doing, any error in the determination of its length, or in the levels, would be negatived. It was only necessary that the two ends should be driven in the same line,—they would be sure to meet sooner or later. This was on the supposition that the two gradients would be maintained until the two ends met. The whole of this advantage is going to be sacrificed. If there is any material error in the determination of the length or of the levels, the two ends may not meet. One has not to go farther than the summit of the Mont Cenis pass itself to show that errors may creep into trigonometrical work, even when it is conducted by distinguished engineers. The height of that pass has been obtained by two independent surveys; one, carried through Trance from the level of the sea, and the other carried through Italy from the level of the sea; yet the Italians make the summit 59 feet higher than the French.

When the great tunnel of the Alps is completed, will it be a useless marvel? or will locomotives be able to work in it? Will the trains arrive at the ends with cargoes of asphyxiated passengers who will have to be revived with draughts of compressed air? or will there be no trouble on account of ventilation? It must not be argued that because it is impossible for locomotives to work in the tunnel at present, it will be impossible for them to work in it when it is completed. The temperatures of the two sides will frequently be different, and that alone will produce considerable