CHAPTER XXII.
TUNNELS.
Subterranean London—The Mont Cenis Tunnel—Its Length—Ingenious Boring Apparatus—The Grotto of the Pausilippo—The Tomb of Virgil.
The most renowned subterranean works of previous ages are generally of a religious character, as they have been executed to serve either as resting-places for the dead, or as temples in which gods or saints were worshipped. Thus the rock-tombs of the Egyptian Pharaohs and the sacred grottoes of India still bear witness to the feelings which conceived and realised the idea of these stupendous excavations.
Our own times furnish no similar examples of underground temples or mausoleums on a scale so grand as to command the admiration of posterity. We neither scoop out whole mountains nor deeply plunge into the entrails of the earth to reverence the dead or to testify our devotion; our subterranean labours all bear the stamp of practical utility. But never yet has the genius of man executed such wondrous excavations as those of the present day; and though the purposes for which they are performed may seem commonplace and prosaic when compared with the ideal aims of the unknown artists who planned the Pharaonic rock-tombs, or the temples of Ellora, yet the boldness of their conception entitles them to rank among the grandest architectural works, while the difficulty of their execution would have appalled the most enterprising engineers of any age.
Modern London alone has more subterranean wonders to boast of than all the capitals of the ancient world. As in the human frame numberless vessels and nerves provide for the circulation of the blood, and convey telegraphic signals through every part, so in the vast body of our metropolis an amazing system of subterranean communication carries off the sewerage of its millions of inhabitants, provides them with light and water, conveys intelligence from one end to the other of its enormous circuit almost with the rapidity of thought, transports thousands of travellers below the crowded streets, and, not satisfied with all these achievements, opens passages under the broad river to which it owes its boundless wealth.
BORING MACHINE IN THE TUNNEL, MONT CENIS.
But even the wonders of subterranean London, or of Paris—where troops moving underground can march from one fortified caserne to the other, so that, in a more literal sense than Pompey, the rulers of France can say that they have but to stamp upon the ground to make legions start up from the soil—are surpassed by those which the railroad calls forth in its triumphal progress through the world. The Alps themselves, with their eternal snows, no longer oppose a barrier to the locomotive; and we have lived to witness the completion of the most gigantic tunnel ever yet devised by man. The borer has slowly but indefatigably done its work in the entrails of Mont Cenis, and the subterranean junction of France and Italy has been at length achieved. The tunnel, which pierces 12,201 metres, or nearly seven miles, of solid rock, opens on the Italian side at Bardonneche, 1,291 metres (about 4,000 feet) above the level of the sea, and on the French side at Modane, at a height of 1,163 metres. From each opening the tunnel gently ascends towards its culminating point in the centre of the mountain, so as to allow the waters to drain off on either side. The direction of the excavations was determined by trigonometrical measurement, which of course required the nicest accuracy, as a deviation of but half a centimetre on both sides would amount to no less than 120 metres in the centre.
BORING MACHINE IN THE SECOND WORKING GALLERY, MONT CENIS TUNNEL.