TUNNELS.

While much which modern research claims as discovery has proved to be what the world had long since forgotten, the construction of highways through mountains and avenues beneath the surface of the earth appears to be able to maintain its claim to originality. Former engineering skill conveyed water over chasms by expensive aqueducts; and the causey of King Solomon and the roads of the Incas of Peru, are examples of the former progress in this art of makingway over the gulfs which are sometimes apparently impassable. But the present method is bolder and more aggressive. Instead of "overturning mountains from their roots," they are pierced through their very centre. Chicago has done a greater feat; that of burrowing under the bed of Lake Michigan for a distance of two miles, to obtain a supply of water pure from the contaminations of foreign matters, and ample for the wants of the millions that are yet to make up the population. London has descended below the surface of the earth to excavate a thoroughfare, and even bridged the river Thames from beneath for the purpose. Now, the people of Chicago are preparing another tunnel under their river, and the capitalists of England are estimating the feasibility of a tunnel and railway under the Channel from Great Britain to France. In a former geological period the sites of London and Paris were under the same lake; how great the contrast if they should be connected by a subterranean and subaqueous railway.

Mr. Hawkshaw, one of the most successful engineers of the United Kingdom, has actually employed two years upon an investigation into the subject of effecting a submarine passage across the English Chanuel. Borings have been made in the neighborhood of Dover, and likewise between Calais and Boulogue, and also in the mid-channel, to ascertain the geological structure of the crust of the earth, and the practicability of the enterprise. We have not heard of his conclusions; but he proposes the construction of a tunnel which will communicate on the French side with the North of France Railway, and on the English side with the Southeastern and London, Chatham and Dover railways, so that there will be an unbroken line of railway communication between London and Paris. The excavation itself would be made from both ends; also from shafts in the channel. At the top of the shafts powerful steam engines would be erected for pumping, for drawing up the excavated material, and for supplying power to the machinery employed.

Mr. Joseph Dixon, of the city of New York, has patented a mode of constructing submarine and underground railroads that deserves favorable attention. His plan is to have a tunnel of iron cast in parts and sections, each part and section to vary as circumstances may require. For an underground railroad he would excavate the earth from the surface to the required depth and width; lower the various parts and fit them. For loose or watery scil, or in the case of a subaqueous railway, the sections would have closed sides; the arch and sides to be supported by columns or ribs when necessary, and the joints to be by tongue and groove, and to have felt or sacking between them, so as to render them watertight.

In this way both the Hudson and the East river could be traversed

from beneath with ease, safety and celerity, which are not practicable with our present ferry-boats. Mr. Dixon is now pressing this mode of construction upon the members of the " West Side Association," and others interested in the project of a Broadway Underground Railroad.

The most magnificent tunnel scheme of the age, if not in the history of the world, however, is the Lake Tunnel of Chicago. We can think of no analogous undertaking to compare with it, except the Cloaca of Rome, constructed in the pre-historical period, for the draining of the lake and marsh which obstructed the growth of the city. The tunnel was obtained by the amended charter of Chicago, approved February 13th, 1863, and by act of Congress, approved January 16th, 1864. A Board of Public Works was created, with power to carry it into effect. The contract was awarded for $315,139; and the ground selected for the commencement of the work at the foot of Chicago Avenue. Ground was broken on the 17th of March, 1864, with appropriate ceremonies. After sinking a shaft the required depth, and lining it with an iron cylinder to protect it from the shifting quicksand, the work of tunnelling from the shore end was proceeded with.

From the shore shaft the tunnel extends two miles in a straight line at right angles to the shore. Its width is five feet, and the height five feet and two inches; the bottom and the top arches being exact semicircles. It is lined with brick masonry eight inches thick in two rings or shells; the bricks being laid lengthwise of the tunnel, with toothing joints. It had been contemplated by the contractors to make the brick for this purpose from the clay excavated by the workmen ; but it was found to be full of little calcareous stones, which on burning were transformed into quicklime, rendering the bricks unfit for use. The bottom of the tunnel is 66 feet below water level, and has a gradual slope toward the shore of two feet per mile, which enables the emptying of the tunnel in case of repairs, the water being shut off by means of a gate. The work has been laid in brick eight inches thick all round, well set in cement. The lower half of the bore is constructed in such a manner that the bricks lie against the clay; while in the upper part they are wedged in between the brickwork and clay. This prevents any dangerous reresults from the tremendous pressure, which it has been apprehended might burst in the tunnel.

On the 24th of July, 1865, the crib for the eastern end of the tunnel was launched, towed out, and sunk in its place; Governor Oglesby and other citizens being present. On the 31st of December, the workmen having sunk the shaft, began to excavate toward their fellows, who had dug their way 4,825 feet from the shore. Their progress has been uninterrupted; and so perfect were the calculations of the engineers that when the two excavations met, on the 27th of November, they varied but nine inches from a right course, and one inch on the bottom.

What now remains is to remove the tramway used by the workmen, cleanse the tunnel, and arrange for the introduction of the water. For this latter purpose the top of the cylinder at the crib will be covered with a grating to keep out the floating logs, fish, etc. A sluice will be made in the side to let in the water, and a light-house built above to protect the crib from injury by vessels, and at the same time show the way to the harbor of Chicago.

The tunnel will deliver, under a head of two feet, twelve million

gallons of water daily; under a head of eight feet, thirty-eight millions, and under a head of eighteen feet, fifty-seven millions. The velocities for these quantities will be 1.4 miles per hour under a head of two feet; 2.3 miles under a head of eight feet, and 4.2 under a head of eighteen feet. It will be competent, under the latter conditions, to supply a million of people daily with fifty-seven gallons each. The cost of this work has been about six hundred thousand dollars.

The people of Chicago have now undertaken another enterprise; that of a tunnel under the river. The contractors have agreed to finish the tunnel for $271,646 04. They propose to complete it in March, 1868. The tunnel is to be on Washington street, about 1,800 feet long, and resting on a foundation of concrete two feet thick. The masonry will be protected by a heavy sheathing of lead. That part of the tunnel beneath the bed of the river will be thirty-two feet below low water mark. It will be constructed in sections in coffer dams, so as to obstruct the channel of the river as little as possible. There will be two passage-ways for trains, eleven feet wide and fifteen feet high, and in the part under the river will be also a passage way to be reached by stairs at each end. The project is the first of the kind ever attempted in the United States. In London the tunnelling enterprise has been perfectly successful. There were engineering difficulties to overcome such as are hardly to be expected elsewhere, the expansive character of the clay, the frequent occurrence of beds of sand and gravel, the sewers and drains-particularly the Great Fleet sewer, the gas and water pipes, the Grand Junction Canal, etc. But it was done at a total cost of $14,000,000, or $5,500,000 per mile, including the outfitting and stocking of the railway. The enterprise yields dividends; 5 per cent in 1863; 61 in 1864, and 7 per cent in 1865. The number of passengers carried in the first six months of 1863 was 4,823,457; in six months of 1864, 5,104,385; in six months of 1865, 7,462.823; in six months of 1866, 10,303,305. The revenue has increased; in the first six months of 1863 it was £53,058, and in the first six months of the present year, £102,947. These figures would seem to demonstrate the feasibility of the proposed tunnel under Broadway as a remunerative enterprise.

The excavation of mountains to permit the carrying through them of railroad tracks is now a matter of every day occurrence. We may very properly denominate this the Tunnel Age. The Appenines of Italy, the mountains of Provence, the numerous hills of England and Wales have been disembowelled for this purpose. The Bergen Tunnel, near Jersey City, is the admiration of engineers. The Sand Tunnel on the Pittsburg and Connellsville Railroad has just been cut through, a length of 4,700 feet, a thousand more than the long tunnel on the Pennsylvania Central Railway through the Alleghanies between Altana and Cresson. A tunnel is projected through the Sierra Nevada in California, a length of 1,700 feet for the accommodation of the Pacific Railroad; and fourteen months have been assigned for the time to be consumed in the undertaking.

The Hoosac Tunnel, considered by many to be the Massachusetts Folly, is after all the greatest bore of the Western Continent. Under the auspices of Governor Andrew, the State of Massachusetts has undertaken the work, and is prosecuting it with energy. The cost has been more than three millions of dollars, a pretty serious matter for a little common

wealth of a million and a quarter of inhabitants, and as much more will be required. But it will go through.

The tunnel now in progress under the Alps at Mont Cenis is the bold. est work yet undertaken. Heretofore the iron horse had not been able to emulate Hannibal and scale this barrier, although this may yet be done; but the engineer is fast opening for him a way without filling up the valley or bringing low the mountain. When finished it will be a lasting monument to the statesmanship of Cavour. At the time of the cession of Savoy to France ten million francs had been expended in the work; sixty-five millions being the estimate for the whole. A convention between the Governments of France and Italy reserved the right to the latter country of completing the tunnel, both countries dividing equally the expenditure. In the event of the earlier completion of the work than the time contemplated, France will pay a premium. A short time since it had reached 7,600 feet on the French side and 11,800 on the Italian. A thousand workmen are employed at each end of the perforation, divided into three gangs relieving each other every eight hours. They were making their way through quartz at a very slow rate; but the engineers were hoping to reach gypsum, when the work might go on faster. The entire extent of the proposed tunnel is 12,220 metres, of which on the first day of January last 6,900 remained to be perforated. Unless unforeseen circumstances happen, it is hoped that the entire perforation will be completed in three years more, and that the tunnel will be passable from one end to the other on the 1st day of January, 1870. There lies an obstacle, however, in the way of the construction of these tunnels which bids fair to preclude future undertakings of the sort. They are too costly for private enterprise to undertake them. The tunnel through the Alps would never have been undertaken except for the boldness of Count Cavour, backed by the treasury of the Sardinian, afterward the Italian Government, aided by subventions from France. The Hoosac Tunnel would have been abandoned by the company undertaking it but for the aid granted by the State of Massachusetts. The improvements in the construction of railways and rolling-stock enable the ascent of mountains to be made. A road has already been constructed over Mont Cenis, and is about ready for travel. A part of it which has been already completed on the slope along the carriage road was passed over by a train consisting of several carriages at a rate of 11 miles an hour in ascending, and 9 in coming down. The incline sometimes attains 8 feet in the one hundred, and some of the turnings have a radius of only 133 feet.

Great as the importance of those projections will be to travel and commerce, there is likelihood that future undertakings of this character will be superseded by improvements in railway construction.

It has been suggested by engineers that a railroad over Hoosac Mountain would be feasible, which would, if it did not supersede altogether the occasion for the completing of the tunnel, answer for use till that event should take place. The plan of Mr. Fell for the application of steam traction to ordinary carriage-roads would answer this case admirably. Nevertheless, with all these advantages of economy of construction and earlier completion, our preference remains for the tunnel, wherever it shall be practicable, as being cheaper in the long run, safer to use, and of more permanent benefit.

RAILROAD EARNINGS FOR NOVEMBER.

The gross earnings of the following railroads for the month of November 1865 and 1866 comparatively and the difference (increase or decrease) between the two months are exhibited in the following statement:

The earnings of the Erie Railway for November, 1866, do not include those of the Canandaigua & Elmira Railroad which, since November 1, has been operated under contract by the Northern Central Company. Had these been included the decrease would have been much less than

is apparent.

The earnings of the same roads for the eleven past months of the same years, are shown in the following tabulation:

Railroads.

Atlantic & Great Western.

Chicago, Rock Island & Pacific.

3,221,208

3,119,278

Dec. 101,930

Erie (including Buffalo Division).

Dec. 1,433.736

Illinois Central.

6,664,!20

Marietta and Cincinnati.

1,080,357

Michigan Central.

4,175,677

1,113,851 Dec. 33,494 3,851,401 Dec. 324,276

Michigan Southern

3,773,408

3,703,193 Dcc. 70,215

Milwaukee & Prairie du Chien.

1,875,808

1,885,545 Inc. 9,737

Milwaukee and St. Paul..

Ohio and Mississippi

Pittsburg, Ft. Wayne and Chicago..

2,363,876 2,405,870 Inc. 41,994 3,508,686 3,098,970 Dec. 409,716 7,908,099 6,904,822 Dec. 1,003,277

Toledo, Wabash and Western..

Western Union.....

2'679,655

3,430.234

Total (16 roads) ...

Dec.$1,881,712

$69,875,011 $67,993,299

The aggregate earnings of these sixteen roads for November, as compared with those of the previous month, show the following result:

The net aggregate result of the eleven months shows a falling off from the same months last year of $1,881,712, or 2.66 per cent. The decrease of November, 1866, from November, 1865, is 2.51 per cent.