no serious accident from earth, gas, or water, occurred in the whole course of the work.

The soil has been found to be so uniform that only one leakage of water through the tunnel ever occurred, and that only distilling through a crevice at the rate of a bucketful in five minutes. This occurred in September, 1865. The workmen left in dismay, but soon returned and repaired the crevice. From that time no accidents of any importance have occurred to hinder the progress of the work, with the exception of one or two slight escapes of gas, which resulted in nothing serious. Several stones, varying from the size of an egg upwards, have been met with, but very few in comparison with the great mass of clay. The only fault to be found with the clay was, that it contained too much calcareous matter to make good bricks. The contractors claim that they have lost money on this account. The bricks formed of the clay found in the tunnel would not burn solidly, so that they were obliged to get bricks elsewhere.

The lining of the shore-shaft consists of twelve inches of the best brick and cement, in three shells; about 4,000,000 bricks were used in its construction.

On the 16th of November, 1866, the opposite gangs of workmen were within two feet of each other, and this partition was broke through on the following day in a formal manner by the Board of Public Works. The accuracy of the measurements of the engineer was such, that the two lines of excavation coincided in the centre within nine and one-half inches, and the floors joined with a difference of only one inch.

Water is to be let into the lake-shaft by three gates, on different sides, and at different heights. The lowest is five feet from the bottom of the lake; the next ten feet, and the highest fifteen feet. Flumes through the surrounding masonry, also closed by gates and gratings at their outward ends, will conduct the water to the shaft gates. All the gates can, of course, be opened and closed at pleasure.

The tunnel, as now constructed, will deliver, under a head of two feet, 19,000,000 gallons of water daily; under a head of eight feet, 38,000,000 gallons daily, and under a head of eighteen feet, 57,000,000 gallons daily. The velocities for the above quantities will be one and four-tenths miles per hour, head being two feet; head being eight feet, the velocity will be two and three-tenths miles per hour; and the head being eighteen feet, the velocity will be four and two-tenths miles per hour. By these means it will be competent to supply one million people with fifty-seven gallons each per day, with a head of eighteen feet. With regard to the character of the work, the material met with in the process of excavation has been stiff blue clay throughout, so that the anticipations of the contractors have, in this respect, been fulfilled.

The crib, since it was sunk and loaded, has been thoroughly tested by violent storms, and, during the winter, by the moving fields of ice. It withstood the shocks, both of the ice and the storms, without injury, and the least movement of it, since it was fairly loaded, has not been discovered.

TUNNEL UNDER THE ENGLISH CHANNEL.

Mr. Hawkshaw has been engaged in making trial borings with a view to develop a project for a railway tunnel under the channel between Dover and Calais, and communicating on the English side with the Chatham and Dover Railway, and on the French side with the Northern Railway of France. He proposes to carry on the excavations for the tunnel from both ends, and also from shafts in the channel, at the top of which powerful engines will be erected for pumping and winding up the excavated material, and for supplying motive power to the machinery by which the excavation is effected.

On the other hand, Mr. George Remington is of opinion that a tunnel on the site proposed by Mr. Hawkshaw is impracticable, on account of the difficulty he anticipates in keeping down the water in a chalk excavation of that magnitude. He therefore proposes another line for the tunnel between Dungeness and Cape Grisnez, which, entirely avoiding the chalk, passes through the Wealden formation, consisting chiefly of strong clay. The tunnel would be twenty-six miles in length from shore to shore. On this route in mid-channel, there is an extensive shoal, with only eleven feet of water upon it at low-water spring tides, where Mr. Remington proposes to construct a shaft protected by a breakwater.

CHICAGO RIVER TUNNEL.

A tunnel has recently been commenced at Washington street, on the south branch of the Chicago river. It is to consist of three passage-ways, the centre one to be used by foot-passengers and the two side ways to be used for vehicles. The middle passage will be 15 feet high and about 10 feet wide, each of the outer passage-ways being 11 feet in width by 15 feet at the highest point. The width of the river at Washington Street is about 180 feet, while the whole length of the tunnel, after providing for a suitable inclined plane at each entrance, will be about 945 feet. The floor of the tunnel at the centre of the river will be about 32 feet below low-water mark.

The tunnel is to be constructed by means of coffer-dams, which are to be placed, with their protections, up and down the river, within a space, north and south, of not over 150 feet, and, east and west, of not over 100 feet, so as to have a space of nearly 50 feet for the passage of vessels entirely unobstructed. Upon the completion of the work, such portions of the dams as may remain will be entirely removed, so as to leave the river as unobstructed as at present. The tunnel proper is to be formed of the most perfect brick and stone masonry, backed with concrete, while the floor of roadways will be neatly paved with Nicholson pavement. The work is to be completed in March, 1868.

Should this latter work prove a success, we may look for the general adoption of the tunnel instead of the bridge plan at all our river crossings; and, as a consequence, the absolute freedom

of the river to sailing craft of all descriptions, thus avoiding the almost interminable delays now caused by the constant swinging of the various bridges during the season of navigation, as well as the many accidents which are sure to result from our present bridge system.

The longest tunnel in England is the Box Tunnel on the Great Western Railway, which is 9,680 feet long, 39 feet high, and 35 feet wide.

SAND-PATCH TUNNEL.

The miners working in the middle section of the Sand-Patch Tunnel, on the Pittsburg and Connellsville Railroad, have met, thus piercing once more the great mountain barrier between the Ohio valley and the sea-board. The Sand-Patch Tunnel is 4,750 feet long, or 1,000 feet longer than the Alleghany-Mountain Tunnel of the Pennsylvania Railroad. It was commenced some ten years ago, is to accommodate a double track of rails all through, being 22 feet wide, and 19 feet high. The greater portion of it goes through solid red sand-stone, not requiring any brick arching for that distance. The grade of the tunnel is 2,200 feet above the level of the sea, or 1,500 feet higher than low-water mark of the Ohio river at Pittsburg.

THE MONT-CENIS TUNNEL.

It is estimated that the number of holes which have to be drilled by the rock-boring machines in the Mont-Cenis Tunnel, before that work is completed, is about 1,600,000. The total depth of all these holes when bored will amount to about 4,265,890 feet, which is 105 times the length of the tunnel. Nearly 13,000,000,000 blows will be struck by the perforators, to do this work. The entrance to the tunnel, on the French side, is 3,946 feet above the level of the sea, and its termination, on the Italian side, 4,380 feet, so that the actual difference of level between the two extremities is about 434 feet.

The total length of the Mont-Cenis Tunnel is 12,220 metres; of this, 7,977 remain to be made. Having been begun in 1858, and with new methods and energy in 1863, 4,423.4 metres were finished on the first of April, 1865; of which, 1,646 metres were accomplished by the old methods of tunnelling, and 2,777.4 by the new mechanical methods, since the commencement, of 1863-802 metres in 1863; 1,088 in 1864; and 337.4 in the first quarter of 1865. The rate of progress in 1862 was 2.02 metres per day; in 1864, 2.92 metres, and in 1865, thus far, 3.75. At the last rate, it will take 5 2-3 years to complete the tunnel.

Air is compressed by water-power outside, and is conveyed by pipes into the excavation, where it gives motion to the chisels that perforate the rock, forming cavities for the gunpowder used in blasting. Small perforators travel on a carriage, each of them being a kind of horizontal air-pressure engine, the prolonged piston-rod of which carries a jumper, that makes 250 strokes a minute. The excess of pressure on each jumper, above that of the air-spring which brings it back, is 216 lbs., thus bringing a very considerable power into action.

THE FRENCH CANAL AT SUEZ.

It is announced that in 1867 the long-projected canal through the Isthmus of Suez, will be opened to the world. In this great enterprise, the French have once more shown their extraordinary control of persons of totally opposite characters and habits of life, and have, moreover, exhibited the business faculty in a degree rarely shown by other than Englishmen. There are now working at the canal nearly 19,000 men, of whom 8,000 are Europeans, and the remainder Arabs, Egyptians, or Syrians. The crews of the dredging-machines are often composed of Frenchmen, Italians, Greeks, Germans, Egyptians, and Maltese; and we are assured that they are in no way inferior to the more homogeneous crews which are seen at home. The Orientals even exhibit a zeal and ardor which almost equal the activity of Frenchmen. The arrangements for the housing, feeding, and sanitary welfare of the workmen are, seemingly, very complete. There is free trade in provisions, and 1,490 traders have established along the line of works, hotels, canteens, warehouses, and shops, where almost everything can be obtained. The medical, postal, and telegraphic services are under the control of the company. At great expense, a water supply has been obtained, which yields 2,000 cubic metres per day. The district is destitute of watercourses, and this arrangement was, therefore, of the highest importance. By these means, cholera and other maladies have been warded, off. From the measures taken by M. de Lesseps and his colleagues, for the comfort and health of the workmen, we might learn a lesson. In India, China, and the colonies, we have army "stations," which are regularly occupied during certain seasons of the year, and which are yet without proper house-room and pure water.

But beyond these things, the mechanical contrivances which have been invented, and are now used, for the several different kinds of work, are worth consideration. Conspicuous among them are the dredging-machines. To cut a channel through a certain piece of land, the plan adopted has been to dig by hand until sufficient depth and width has been secured to float a dredging-barge, when the water has been let in, and the machine set in motion. Instead of emptying the mud into another barge, to be taken out to sea and there discharged, each dredge has affixed to it a long spout, the upper end of which begins on the dredge itself, as high as possible, where it receives the earth raised by the buckets. At the same time, pumps worked by the steamengine of the dredge raise a torrent of water which carries the earth off beyond the bank, and spreads it over a wide surface. In this country, where we are just now about to reverse our system, and keep our rivers clear instead of filling them with deposits, a modification of this machine would be of great service. By its means we might at once deepen and clear the beds of our rivers, and add materially to the fertility of the adjacent fields. Few things are more fertilizing than what is called "warp," and by the means thus pointed out, this could be obtained artificially.

In many places in England, a plan not unlike that by which the valley of the Nile is made fertile, is carried out. In Yorkshire, for example, it is a regular practice to open the banks of the Dutch river, and allow its turbid waters, which contain much soil in suspension, to spread over the fields. When the gap is closed, and the water drawn off, a rich alluvial mud remains, on which splendid crops are raised. The system of opening the banks of the river is, however, awkward and expensive. The Suez canaldredge does away with its necessity, and applies scientifically what is now obtained by a very clumsy system. — London Star.

The Malta "Observer," of a late date, says: "By reliable information, recently received, we learn that the works of the Isthmus of Suez Canal are being very actively carried forward by M. de Lesseps. An average depth of from seven to nine feet has been obtained from Port Said, along the salt-water canal; and the rest of the distance to Suez is traversed temporarily by a fresh-water one about seven feet deep, connected with the other by means of locks and powerful pumps. As far as sixty stations the full width of the proposed ship-canal has been excavated to sixty metres; but from that point to the seventy-fifth station and Ismalia, the width is incomplete. All that has been done is done well, and reflects the highest credit on the science, skill, and persevering energy of the French engineers. The real difficulties of dredging in a constantly dissolving sand are now commencing; but well informed persons entertain but little doubt that these and all others may be overcome by time and money.”

FRITH OF FORTH BRIDGE.

Parliamentary sanction has been obtained for a bridge over the Frith of Forth, of a magnitude which gives it great scientific interest. It is to form part a of connecting link between the North British and Edinburgh and Glasgow Railways. Its total length will be 11,755 feet, and it will be made up of the following spans, commencing from the south shore: First, fourteen openings of 100 feet span, increasing in height from 65 to 77 feet above highwater mark; then six openings of 150 feet span, varying from 71 to 79 feet above high-water level; and then six openings of 175 feet span, of which the height above high-water level varies from 76 to 83 feet. These are succeeded by fifteen openings of 200 feet span, and height increasing from 80 to 105 feet. Then come the four great openings of 500 feet span, which are placed at a clear height of 125 feet above high-water spring tides. The height of the bridge then decreases, the large spans being followed by two openings of 200 feet, varying in height from 105 to 100 feet above high water; then four spans of 175 feet, decreasing from 102 to 96 feet in height; then four openings of 150 feet span, varying in height from 95 to 91 feet; and, lastly, seven openings of 100 feet span, 97 to 92 feet in height. The piers occupy 1,005 feet in aggregate width. The main girders are to be on the lattice principle, built on shore, floated to their position, and raised by hydraulic power. The total cost is estimated at £476,543.Engineering, Jan. 5, 1866.