face. The cost was about $400 per running yard.

The Nerthe Tunnel in France, is nearly three miles in length. For nine hundred and fifty yards of its length it is in rock cutting, where arching was unnecessary. The remainder is lined with masonry. Twenty-four shafts were sunk, varying in depth from sixty-five to two hundred and sixty-two feet. The work was completed in three years, and cost $412 per running yard.

The Tunnel of Rilly, on the line from Paris to Strasbourg, is a little more than two miles long. Eleven shafts were commenced, two of which were abandoned on account of the abundance of water, the others were completed. In some of the shafts the water was so troublesome that it was necessary to use for curbs cast iron cylinders, five feet in diameter, and about three feet long, bolted together. The time consumed in the construction of this tunnel was three years and four months. It passes through a chalk formation, which was, in some places, so seamy, that great precaution was necessary to prevent the falling in of large masses. The cost was $432 per running yard.

Mr. Storrow visited and examined several other French tunnels, and his reports upon them are full of interest; but the abstracts given are sufficient to show the various obstacles and difficulties encountered by the English and French engineers in the prosecution of their work, as well as the cost, and the success which rewarded their skill and perseverance. We now come to the great tunnel under the Alps, the most remarkable and gigantic enterprise ever attempted in civil engineering. Our facts in regard to it are derived from Mr. Storrow's report, (which it will be remembered was made in November, 1862,) and from a very able account in the Edinburgh Review of July, 1865.

The object of this work is to connect France and Italy, by a continuous line of railroad, by piercing the great Alpine barrier which separates Savoy from Piedmont, and thus connecting the valleys of Rochmolles and the Arc. When the scheme was first suggested it seemed like a dream of enthusiasts. The distance would be more than seven miles. No shaft could be sunk, as it was estimated that it would take forty years to reach by that means the line of the axis of the tunnel. The gallery must then be constructed by horizontal cutting from the two ends. How were the workmen to breathe? What chasms, unfathomable abysses and resistless torrents might not be encountered? Was it certain that the two sections commenced from the opposite ends would not miss and pass each other in the middle of the mountain? But as the subject was more thoroughly discussed, these doubts and fears seem gradually to have faded away, and a conviction took possession of the public mind that such a tunnel was practicable. This conviction at last assumed form and development through the genius of Messrs. Sommeiller, Grattoni and Grandis, three young Italian engineers, who have won for themselves a nobler fame than that of either of the great generals who led their armies over the Alps. It was their good fortune to have secured the confidence of one of the most enlightened statesmen of modern times, Count Cavour, the energetic minister of Victor Emanuel, who, throughout all the doubts, perplexities and embarrassments attending the first stage of a new and bold enterprise, exposed to criticisms, sometimes ignorant, sometimes malevolent, on the part of politicians and professional men, gave these engineers his "constant, earnest and sanguine support and encouragement."

It appears that an English engineer had patented a machine for drilling by steam, by means of which the drills were darted forward against the opposing rock with great velocity and force. But steam could not be used in the tunnel, where the great desideratum is a supply of fresh air. In the meantime Messrs. Sommeiller, Grattoni and Grandis had turned their attention to the question of compressed air as a motive power, and after a long series of experiments; gave to the world as the result of their joint ingenuity, a machine which acts simply by the force of air reduced to one-sixth of its ordinary volume, by means of the pressure of water. The quick perception and practical genius of our three engineers soon enabled them to combine their machine with the perforating apparatus above named, so that the compressed air took the place of steam, and performed its work perfectly. This combination is the machine which has been in successful operation under the Alps since June, 1861, and which, greatly improved and perfected by Yankee ingenuity, is about to be applied to the Hoosac Mountain.

Before proceeding to give some account of the Alps Tunnel, it should be stated that it is a national work, and not a commercial speculation. It was originally undertaken by Sardinia, within whose territorial limits it was then wholly included. The cession of Savoy to France brought nearly half the tunnel into French territory, and by the convention establishing the new boundary between France and Italy it was stipulated that this great national work should be continued, should remain exclusively under the control of the Italian engineers, and that France should pay into the Sardinian treasury its proportion of the cost, according to an estimate then made and considered final, and fixed at 3000 francs for each running metre, equivalent to $550 for each running yard of its length in French territory. The work has remained, therefore, as it was, under the exclusive direction of M. Grattoni and M. Sommeiller, the engineers; and a French commission visit the work from time to time, by order of the French government, to view its condition, ascertain its progress, and vouch for the amount to be paid to Sardinia.

It is hardly necessary to give a detailed description of the mode by which the compressed air is made to act on the perforating machines at Mount Cenis. The problem was how to get a constant equable supply of air compressed to one-sixth of its ordinary bulk. To effect this a reservoir was constructed at Bardonneche, elevated to a height of eighty-two feet above the works, which furnishes a moving force of two hundred and eight horse power, that being all which is required to operate the drills and ventilate the tunnel. The reservoir is supplied by a never failing mountain stream. From the compressing works, the air is conveyed in a pipe into the tunnel to the drilling machines; another pipe conveying water to wash out the drill holes. At the Fourneaux end of the tunnel, the reservoir is supplied with water by means of pumps.

The compressed air and water being ready for their work, an iron frame containing the perforating needles moves along the rails and confronts the rock which is to be attacked in the gallery or heading. The frame is armed with nine or ten perforating machines arranged so that the greatest number of holes can be bored in the center of the opposing mass of rock. To each of these are attached flexible tubes, one containing the compressed air which drives the drills, and the other water, which is injected into the holes as they are bored. The machine consists of two parts; the one a cylinder for propelling the drill, by means of a piston, and the other a rotary apparatus for working the valve of the striking cylinder, and turning the drill on its axis at each successive stroke. To bore eight holes of the required depth, the piston rod gives 57,600 blows. The action of each machine is independent of the other, so that if one of them is broken, or gets out of order, that of the rest is not delayed. The drills act at different angles so as to pierce the rock in all directions, and when the requisite number of holes have been drilled, the iron frame is pushed back, and the central holes are charged and exploded. The smaller surrounding holes are then charged and fired. At each blast, a strong