forms a natural fosse, surmounted by a fortress, now dismantled, built by the Sardinians to guard the pass. This fort is on the side of the gorge opposite the road, with which it is connected by a light iron bridge, called the "Devil's Bridge." It looks like a slender thread stretching across the chasm. On the right side is seen the railroad train toiling up one of the steepest ascents. Here is one of the most striking views on the route. The remaining illustrations tell their own story. it would be hard to find. We never before saw so many people afflicted with that ugly, wenlike excrescence, the goitre, and its accompaniment, apparent idiocy. But the scenery is magnificent. Above us rises the Grand Vallon, its upper portion white with snow; while, lower down, the cliffs are clothed with firs and pines, looking, in contrast with the snow, almost black. Lower still are trees and shrubs, whose foliage, clad in bright autumnal hues, reminds us of what we have seen among our own White Mountains of New Hampshire. But far higher above-almost twice higher than Mount Washington-are piled the Alpine peaks, soaring one above another, and shutting in the vision at either extremity of the valley. In six hours after leaving San Michel we reach the foot of the mountain on the opposite side of the Alps, where the Fell Railway terminates, at the little town of Susa, at the head of the broad valley of the Po. Thence a ride of thirty miles, accomplished in an hour, brings us to the gay, bustling city of Turin. Here, repairing to the office of the "Direzione Tecnica del Traforo delle Alpi," we present our credentials and receive a permit to visit the tunnel on an off day; and also a special letter to Signor The idea of the tunnel appears to have been Genesio, the local superintendent, which will first broached, about 1832, by M. Medail, a Piedsecure to us every facility for a thorough exam-montese, born at Bardonnêche, who pointed out ination of the work. Here let us gather up what, during a three days' stay, we learn, by the abundant courtesy of the officials, of the origin and mode of construction of the tunnel which we are to explore. where lay the least thickness of the Alps beThe Italian terminus of the tunnel is less tween Piedmont and Savoy. Ten years later readily accessible than the French one; so we he presented to the Italian government a plan retrace our way to Modane, and walk over and for a tunnel through the ridge. Two engineers, up to Fourneaux, a little village dug in, as it MM. Maus and Sismonda, were thereupon apwere, upon the steep hill-side. A more un-pointed to investigate the matter. After four pleasant place, filled with less pleasing people, years they reported favorably upon the line which has been adopted. The great difficulty lay not in the fact that it must run so far beneath the summit of the mountain; since, for all practical purposes, it made no difference whether this towered half a mile or five miles above. Either distance would equally prevent perpendicular shafts from being sunk to the level of the line, so that the working could be carried on simultaneously at many points. The mountain could be attacked only at its opposite sides, from which the two ends of the tunnel, wellnigh eight miles apart, must be driven toward each other. Moreover, how were the hundreds of laborers to be supplied with air, which could only reach them for almost four miles underground? Again, as far as was then known, only human labor could be employed. Steampower was out of the question; for the steamengine must have fire, and fire must have abundant air, as well as coal and water. It now seems strange to us that, with the knowledge then existing, the work should ever have been seriously considered. Looking back upon the work done, we may safely say that, by no means known to man in 1855, could the excavation of this tunnel have been performed in half a century. Only so many men at a time could work within the contracted space. Unless some mechanical means of drilling other than that of steam-power should be devised, the work, if undertaken, must have been abandoned before it had been a quarter completed. But, as it happened, about 1850, three young Italian engineers - Sommellier, Grandis, and Grattoni-were engaged in a series of investigations. They had no thought of the Mount Cenis Tunnel, with which, however, their names have come to be inseparably connected. All that they then thought of was a means of propelling, by means of compressed air, railway trains up a steep incline among the Apennines. The idea was to use compressed air as the motive power. The principle upon which they started was one already well established—that air, when compressed, has a great expansive and elastic pow- | er. This principle is well shown in the toy known as the "air-gun." The amount of possible force thus to be acquired had long been settled. Air compressed to one-sixth of its natural state has an expansive force of about 84 pounds to the square inch. This is about half more than the pressure of steam in an ordinary stationary engine, as usually worked.* The merest tyro in mechanics need not be told that no machinery creates power. Levers and pulleys and cogs simply enable us to concentrate or apply power already created at the point where we wish to use it; and this transfer is always accompanied by more or less loss. But, as it happened, there was, just where Sommellier and his associates wished to use this We find that the engine which moves the entire mass of machinery in the establishment where this Magazine is printed is usually worked at a pressure of from 50 to 60 pounds. It is safe, however, to increase this by a half. compressed air, a river, which gave abundant force for compressing the air. The problem now became a purely mechanical one. It was merely to transfer the water-power of the river into the shape of condensed air. As we shall see, the same advantage was to be found at each extremity of the proposed Alpine tunnel. About 1855 Mr. Bartlett, an English engineer, invented an apparatus by means of which a drill, driven by steam, was made to perforate a wall of rock to far greater advantage than the same work could be done by hand. His idea was mainly the use of his machine in coal mining in England, where, we believe, it has been and is used to advantage. But, as we have seen, Bartlett's steam-drill could not be used in the Alpine tunnel; while the Italian air-engine was equally unavailable in an English mine, where no water-power for compressing the air was to be had. It occurred to Sommellier and his associates that the two inventions might be combined into one, and used to bore through the Alps. The result of this is shown in what we shall have to see, and explain as best we may. Sommellier and his friends proposed their plan to the Italian government of their day. How the putting this into execution was postponed for years, until the troubles connected with the rise of the new kingdom of Italy got, in a fashion, settled, is a story too long to be told here. Suffice it to say that finally, under the administration of Cavour, somewhere about 1857, the Italian government fairly took upon itself the work of digging the Mount Cenis Tunnel. The first thing was to fix mathematically upon the exact direction which the tunnel should take, so that the two opposite headings should meet under the summit of the Great Vallon. In engineering phrase, the horizontal axis of the tunnel was to be fixed; that is, a line was to be marked out over the crests right under which, no matter how far below, the tunnel should run. In fixing this line the two engineers, Copello and Borelli, to whom the work was confided, encountered great difficulties. They had to scale the rocky sides of cliffs, making paths over untrodden regions, and use their surveying instruments in a region where, at any moment, a sudden storm might interrupt their work. But it was at length* performed, and from the summit of the Great Vallon, 11,000 feet above the sea, down the slope on either side, a line was marked out, right under which the tunnel should run. That the tunnel should nowhere deviate a foot to the right or the left from following this line, lay fairly within the known limits of engineering skill. The compass, carefully used, would settle that. But there was a far more serious difficulty to be met. The two portions of the tunnel must not only approach each other in the same direction, east and west, but they should meet at the same vertical elevation. The precise inclination of the two excavations must be rectified at every rod; otherwise, when they should have met at the centre, one might have been yards or rods above or below the other. There were not wanting those who, up to the very last moment, doubted whether the two workings would ever meet. But the final result, known first on Christmas-day, 1870, showed how accurately all had been done. When the last foot of rock had been broken through, the two excavations struck each other almost to an inch. The first man who passed through the dividing rock, we are told, was Grattoni, one of the three of whom we have spoken. If we could have chosen the proudest three single moments which could | As we pass up to the mouth of the tunnel we mark a human life, one should have been that when Napoleon, at Austerlitz, saw the Austrian line fairly cut in two; another should have been Wellington's, when he saw Napoleon's Imperial Guard tumbling back in rout from its charge upon his solid square; the third should have been that of Grattoni, when, first of all men, he passed through the Alpine tunnel. see this pipe running along the way. We notice the manner in which it is laid, and are inclined to think it absurd. At intervals of three or four yards are low pillars of masonry, upon the top of which is a short piece of pipe, mounted upon rollers. The intervening pieces are braced firmly by iron rods let into the upholding masonry. "What is the use of this ?" we ask of our our pipe were here laid in the usual way, its expansion and contraction under these quick changes of temperature would soon tear it to pieces. We have to make it practically an elastic tube. Now see how our plan works. The ends of the fixed parts, between the pillars, fit into those upon the tops of the pillars, much as one slide of a telescope runs into another. Now when our tube expands by heat, the fixed part is driven a little into the movable part, resting on the pillars; when the tube contracts by cold it is pulled a little out. So our pipe is always of the same length, no matter what may be the expansion or contraction of its several parts. The parts resting upon rollers are made so simply to give free play to the whole. The joints-there are hundreds of them-are made as nearly air-tight as possible by means of rubber or leather packing. So nearly air-tight are they, that the escape of air by all is hardly appreciable. One part in sixty is all that is lost in the whole three miles and more between the reservoir and the place where we are now working. Fairly inside the tunnel, where the temperature is equable, the pipes are laid in the usual way. Don't you see?" At Fourneaux we examine the apparatus for furnishing the compressed air which is to sup-guide. ply the perforating engine, which we are soon to "The temperature of the valley outside of sec at work. What we see is rather simple. the tunnel," he replies, "often varies fifty deClose down at the edge of the Arc is a water-grees in the course of a single day. Now, if wheel, always at work. On the bank above is a huge tank, upheld by a score or so of iron columns. It looks like an ordinary gas-holder. Running up to this are a number of hollow tubes, each opening into the tank by a valve, opening up into the tank, so that every thing going up can pass, but nothing can come back. The wheel drives the water up the tube, forcing the air before it into the tank. When the column of water has reached the top of the tube a valve at the bottom is closed, cutting off the water, while another is opened, allowing that which has entered to pass off; while at the same time another valve at the top is opened, admitting air into the pipe. Then, when the pipe has been emptied of water, the escape-valve is closed and the supply-valve opened, and the rising water again drives the air before it into the tank; and so on perpetually. All this operation, so hard to describe, is easy to understand when once seen. The current of the river turns the wheel; the wheel forces up water into the pipe; this condenses the air contained in the pipe; and so a force which costs nothing, and which for untold ages has lain useless, is made, under human guidance, to work miles away. At Bardonnêche, the other end of the tunnel, they are able to dispense with the water-wheel and the whole pumping apparatus. There, high up on the mountain-side, is a stream which never fails. From this the water is conveyed by pipes into the condensing cylinders, rising when the supply-valve is opened, and falling when it is closed. Otherwise all is the same as we see at Fourneaux. The condensing apparatus at Fourneaux is about half a mile from the mouth of the tunnel. The condensed air is borne from the tank through an iron pipe of eight inches in diameter. We did see, and inwardly resolved that we would not thereafter take it upon ourselves to pass summary judgment upon any engineering question which should come before us in the tunnel. It might be that the engineers were wiser than we. The mouth of the tunnel, which we reach after a walk of half a mile, presents nothing specially notable. It is a mere hole in a hillside, only it looked a little larger than any one which we had seen-say the Bergen Tunnel, near New York. It is a simple horseshoe arch, whereof the height is within a few inches of now?" we ask. "About two miles from the mouth, nearly at the end of the finished part on our side, and close upon that in course of excavation, where you can see how the work is done." Hardly were the words spoken before a gust of smoke dashed full in our faces. "They have been letting off a blast; we shall be just in time to see the work going on." Hitherto we had been walking along what might have been some deserted city street. All at once the way narrowed at the sides and sank down overhead. "Here we are," said our guide, "at the entrance of the gallery in corso di scavazione; for we don't bore this big hole through at once. We make it in three drifts, two side by side, and one at the top; one a bit ahead of the other. The Italians drive the top drift ahead; we put in one of our side ones first." All this was said in such an odd mixture of languages that we are to this day in doubt as to the nationality of our guide. If he was English, he had learned little Italian; if he was Italian, he had learned little English. Could he have been a Yankee who had strayed from the Alleghanies to the Alps? Once or twice we thought his speech bewrayed him. But be he who he might, he evidently understood engineering. We shall hereafter translate his lingua Italiana into English. 66 Why is this?" we ask. "One way of making the drifts must be better than the other. Why not find out the best way, and follow it on both sides ?" twenty-five feet, and the greatest breadth a foot or two more. Wagons, loaded with all sorts of materials, are going in; others, equally laden, are coming out. Fairly within, it is the most dark, damp, and disagreeable place we ever entered, even where the work is pronounced finished. There is, indeed, a solid floor over which to walk; a solid wall of smooth masonry incloses us on both sides. The stones of which it is constructed, we are told, have been brought from miles away, for hereabouts there is no rock which the workmen could hew into shape for such purpose. Each step the way grows darker. We look back toward the entrance through which we have come. It grows smaller and smaller, until at last it is lost to view. Then before, behind, above, and around is utter darkness, broken only by the candles which we carry, and a faint gleam from some gas-light shining like a star in the dis-opposite side; for, before they had run down tance. Meanwhile our guide was profuse in his explanations. "The floor," he said, "looks level; but right in the centre is a covered way, three or four feet high and broad. It was at first designed merely as a conduit for waterpipes and the like. But one day-it was in 1863-when we were working through a rather soft bit of rock, a great fall of rubbish came down, blocking up the tunnel, and shutting in three-score men who were working beyond. They gave themselves up for lost, until one, who had his wits about him, bethought himself of this covered way of escape, through which all crawled out. Since then nobody is afraid of being shut up here." "It is all plain enough when once you come to understand it. The Italian mouth of the tunnel at Bardonnêche had to be a little more than a hundred feet above ours at Fourneaux; and even then we had to make our mouth almost four hundred feet higher than we would have liked to do. You would suppose that the line should have run straight down from one end to the other. That would have answered very well for us, but not for our friends on the half a mile, they would have been flooded. Water in one way or another is always coming into the tunnel; and water, you know, won't run up hill. So, instead of coming down to us, they were obliged to go up a little, to let their water run off on their own side. To make this ascent as slight as possible, they first excavated from the top. When our ends meet at the bottom the water may run which way it pleases. Do you see?" We saw again, and were still further inwardly assured that we had yet something to learn in the matter of engineering. No sooner had we entered the narrow advanced gallery than we seemed to come into a new world. The temperature was certainly As we proceed still onward the air grows high, but the air was pure and sweet, acting hotter. A thermometer hanging by the wall, like balm upon our lungs, which had been lawhich we read by the light of our candle, indi- | boring in the sulphurous smoke. This, as we cates a temperature of 80°. "Where are we soon learned, was owing to the fresh air which, |