The following Table sets forth the progress made on each side since the commencement of the work.

THE TUNNEL OF THE ALPS.

Northern Entrance.Southern Entrance.General Total.
Year.Progress.Total.Progress.Total.
M.[135]C.[136]M.C.M.C.M.C.M.C.M.C.

18571080621.02728725038816460
1858201252575745982
1859132752363536910
1860139502038034330
186119300000019300
186224300....0024300
——————————————————

1861....17001700
1862....38003800
18633760042608020
18644666562120108785
18654584076530122370
18662122981270102499
1867[137]317984566077458
——————183132——————363180——————546312
—————— —————— ——————
275232435680710912

The rate of progress given in the foregoing Table is very different from what was expected previous to the commencement of the works. It was then anticipated that the tunnel would be excavated from end to end before the close of 1864, but it was not until the 15th of October, 1866, or 9¼ years after operations had been begun, that exactly one-half was perforated. On the 1st November, 1867, the half had been exceeded by 1,958 metres, still leaving 4,152 metres to be excavated. The amount of perforation accomplished on the two sides of the mountain has always been unequal, for of the 4,152 metres yet to be excavated, 2,905, equal to about 1⅞ mile, have to be accomplished on the French side, whilst on the Italian there are two-thirds of a mile. This will be understood by an explanation of the strata through which the tunnel is to be carried. Commencing at Modane, there are 2,140 metres of schist, then 363 of quartz, followed by 2,706 of compact limestone, and finally 901 of schist. This completes one half; the other, or Italian half, is all schist. The only rock comparatively easy in working is the schist, but from the commencement the schist on the French side was of a more resisting character than that on the Italian. The miners came upon the quartz exactly where they expected to find it, but instead of its being a stratum 400 metres thick, as was anticipated, it turned out to be only 363 metres; nevertheless, it required two years, less two months, to bring it into subjection, that is, from the 15th of June, 1865, until the 20th of April, 1867,—the progress forward during all that time, not much exceeding half a metre (about 20 inches) a-day. The compact limestone nearest to the quartz having been partly decomposed by the action of this latter, was very workable. Hence, during May and part of June 1867, the advance was very considerable, but since June the compact limestone has proved to be harder but not so difficult to work upon as the quartz. For six weeks the engineers were hopeful that they could go on at the rate of three metres a-day. If such progress could have been unflinchingly maintained, the excavation on the French side could have been accomplished by August 1870. With two metres a-day it will require until March 1872; but if, the advance do not exceed a metre and a-half a-day for two-thirds of the whole distance, the tunnel cannot be perforated under six years, which brings the date to July, 1873.

But the perforation of the rock is not the only serious impediment to progress. All things that live and breathe, miners among the number, require air for their sustenance; and, in order to supply it in sufficient quantities for the support of the human moles within the interior of the tunnel, it has been necessary to resort to special appliances for this purpose. Immense machinery, moved by water-power of an aggregate force for each end of about 400 horses, erected at both entrances of the tunnel, works not only the boring machines, but, at the same time, furnishes the miners with the necessary ventilation. The air is compressed to five atmospheres by means of the water-power just referred to; and the double application of the air is the ingenious contrivance of Messrs. Someilier, Grandis and Grattoni, the distinguished Italian engineers, under whom the works are conducted. Until recently the ventilation, although indifferent except at the site of the boring machines, was excellent in their vicinity; but with each metre that the works progress farther into the mountain, the difficulties of ventilation are added to; especially so on the French side, and for a reason that will at once, on a moment’s explanation, be evident to the reader. When the boring machines have made the usual holes in the rock about three feet deep, they are filled with gunpowder, and exploded. Now, if the excavation of the mountain had been made partly by adit and partly by shaft, as soon as one of the latter had been made, the smoke from each explosion beyond it would have found vent through it to the outer air, and in a few minutes the forward face of the tunnel would be ready for the fresh action of the boring machines. But as there is no shaft in the Cenis Tunnel, the whole of the smoke created by each explosion has only one means of exit—that is, through the tunnel’s mouth. Smoke, in its escape, wants to ascend (as we know by our everyday experience), but it cannot do so for the want of a shaft; it cannot get out even on the level, for the gradient in the tunnel on the French side is, on an average, 1 in 45, or 117 feet 4 inches per mile. As the perforation had, on the 1st November last, been accomplished to the extent of 3,205 metres, the face of the tunnel was about 226 feet higher than the entrance,—consequently, the smoke of each explosion at the present time is not only not able to come out on the level, but it has actually to descend the number of feet just stated before it can commingle with the outer air; and the number of these feet of elevation wall continually increase, until, at the end of the French perforation, there will be 429. We believe it is a matter of fact, that the ventilation is every day becoming worse, and the means of supplying the requisite air are becoming more difficult with each metre of advance made, and so it must continue until the final perforation has been (for no doubt it will be) accomplished.[138] On the Italian half, the rock is throughout, schist, and the gradient, being only one in 2,000, or 2-8/25 per mile, all the elements for progress will continue to be, comparatively, as favourable as they have hitherto been; and even with a much less rapid rate of advance than on the French side, it requires no great gift of prophesy to “forecaste” that the boring machines from Italy will be ready to embrace those from France long before the latter shall have arrived at the midway point. But let it be understood that the works from the Italian side cannot go on a yard beyond midway,—first, on account of the gradient, which would dam up all the water percolating into the tunnel; second, because it would be impossible to keep the line of the tunnel, owing to the absence of all the external landmarks required for ensuring its correct direction. The embrace we have just referred to will take place 4,138 feet above the level of the sea, 1,645 above the level of St. Michel, 429 above the Modane entrance of the tunnel, but only 2-8/25 above that at Bardoneche, 2,360 above the level of Susa, about 5,360 feet below the highest point of the Great Vallon Mountain, and 2,520 feet below the summit of the Mont Cenis Railway.

What might have proved a source of great trouble and expense—water—has fortunately not as yet on any one occasion presented itself in a manner to cause alarm or even uneasiness. We need not therefore refer to this subject in any detail, but before proceeding to as important an element as any with which the tunnel is encompassed—cost—we had better state that the arch of the tunnel is a semicircle 25 feet 3½ inches at its base, 26 feet 3 at its broadest part, and 24 feet 7 inches high. (See diagram.)

Captain Tyler in his report of 1866, sets down the total cost of the tunnel and its 34½ miles of approaches at £5,400,000, or £128,500 per mile. Now we know that up to the present time each metre of tunnel excavated and lined (for it is to be lined throughout from stone quarried near to each entrance, with an occasional introduction of brickwork) costs 7,000 francs, or £280. This would bring its total cost exclusive of permanent way, which would be, say £30,000, to £3,421,600, but we believe that the farther the tunnel is penetrated, the expenses will increase rather in geometrical than arithmetical proportion, and that the average cost of the tunnel will not be 7,000 francs or £280 “per metre courant,” but 10,000 francs or £400. If this be so, the cost of the tunnel, without permanent way, would be £5,188,000. To this sum has to be added the cost of the 34½ miles of approaches. The nature and the probable cost of the works can be appreciated from the fact that they are now about to be let, and the contract time for their completion is to be four years and a-half from the date of their commencement. These 34½ miles of double railway cannot be estimated at less than £60,000 a mile or £2,070,000, making the total cost of the tunnel and of the railways which connect it with the railways of France to the north, and with those of Italy to the south, £7,258,000, or at the rate of £172,800 per mile. Possibly, if the construction were in the hands of a railway company instead of those of two governments, a saving of a million or so might be effected, but in any case the cost would be upwards of £6,000,000, or nearly £142,850 a mile.

In connection with the subject of cost, a calculation of Captain Tyler’s gives the following results. The difference, says the Captain, of elevation between the outer summit of the Mont Cenis Pass and the summit of the railway through the tunnel is 2,520 feet. The excess of working expenses in consequence of this difference of height, estimated on a traffic ten times as great as that which passed over the Mont Cenis in 1865, and the cost of traction per horse power and per hour being taken at 2¼d. (the cost on the Sœmmering and the Giovi), an additional capital of £650,000, or £13,000 a mile, with interest taken at 6 per cent., is represented. If then £13,000 a mile be added to the £21,000 actual cost per mile of a permanent Alpine railway, the total cost of a railway on the mountain becomes, for the purposes of comparison, £34,000 a mile, as against whatever may be the cost per mile for the Tunnel Railway and its approaches. If they cost £142,850 a mile, the comparison will be as 31 to 142; but, if, as we believe, the cost will be £172,800, then the proportion will be at 31 to 172.