as far forward as practicable. By this method the speed of the side motion given to the lower bucket in contact with the bottom remains tolerably constant, although the angle formed by the head chain with the axis of the dredger alters.

The

In conclusion the Author gives the average work done by the steam dredger. This amounted to 90 cubic yards of soil per working hour, as measured in the lighter. The greatest amount of work was 182 cubic yards of light material that can be easily shot from the buckets. The consumption of good West Hartley steam coal is estimated at 23 lbs. for each cubic yard of medium heavy sand soil measured in the lighter; this calculation leaves out stoppages of engine and time for getting up steam. consumption of coal per hour of real working time was 263 lbs.. The maximum F. HP. absorbed was 53.1, when dredging in firm sand mixed with clay, and with full buckets delivered at the rate of thirteen per minute; the minimum F. HP. used was 30 2, with light alluvial soil, and full buckets delivered at the same rate, viz., thirteen per minute. The HP. was calculated from indicator diagrams.

J. J. W.

The Drainage of Lake Fucino.

By A. BRISSE and L. DE ROTROU.

(Le Dessèchement du Lac Fucino, Rome, 4to., 1876, pp. 1–304, and atlas.)

Fucino was the largest lake in Central or Southern Italy, situated in the province of Aquila. It covered the greater part of a vast table-land belonging to the territory of the subprefecture of Ayezzano, a small town rising at a little distance from its shores. This table-land is one of the largest to be met with in the central part of the Apennines, and is surrounded on all sides by spurs of the main chain of mountains, thus forming a vast basin entirely separated from the adjacent valleys, so that the rain waters falling within its limits possessed no outlet by which to discharge themselves into the neighbouring rivers. The area of this basin is 173,000 acres, and the surface waters of the lake on the 10th of June, 1861, stood at 2,094 feet above sea-level. In consequence of the peculiar conformation of this basin, having no communication with any of the adjacent valleys, and the waters collecting in it having no subterranean or other outlet-no means of escape, in fact, but by evaporation or absorption-it frequently happened that, owing to excess or deficiencies of rainfall, the level of the lake either rose or fell beyond its normal levels; in the former case inundating the valleys on its borders, and in the latter producing unhealthiness from its exposed banks. Julius Cæsar

was the first to conceive the idea of draining the lake; it was attempted by Claudius, and the works which he caused to be executed were considered by Pliny as the most extraordinary of that age. The attempt of Claudius was renewed by Trajan and by Hadrian, and in the middle ages by Frederic II., perhaps also by Alphonso I. of Aragon, and by several sovereigns of Naples, but always in vain.

The area of the lake naturally fluctuated from time to time, but its average dimensions were about 37,050 acres. In form it was very nearly elliptical, its greater axis, running from north-east to southeast, was about 12.4 miles long, the shorter one nearly 7 miles. Its bottom sloped very gently downwards from west to east, and at about 7.4 miles from the head of the tunnel constructed by the Romans to drain the lake, the bottom was very nearly level, and constituted the lowest part of the basin. Beyond this level part, the bed rose again towards the east, but with a much steeper gradient. Owing to the amount of earth annually washed into the lake, it was calculated that its bed had risen 15.65 feet since the time of the Emperor Claudius, when its depth is assumed to have been about 53 723 feet.

The most important, as well as the nearest, of the valleys situated on the other side of the mountains which gird the Fucino basin, is that of the Liris, which, to the west, runs parallel for a certain distance with the plateau of the lake, but at a lower level. The river is about 3 miles in a straight line from the lake, but between the two there is a mountain, Mount Salviano, and another plain, called the "Campi Palentini," higher than the lake. As the position of the latter precluded the possibility of making an open cutting between it and the river Liris, the Emperor Claudius determined to excavate a tunnel through Mount Salviano, at about 984 feet below its summit, and under the Palentine fields at an average depth below the surface of 328 feet, in order to discharge the waters from the Fucino into the river Liris at a sufficient height above the latter to enable it, even when in flood, to receive the water from the mouth of the tunnel. This tunnel had its outfall at a level of 41 487 feet above the Liris, and was constructed on a gradient of about 1 in 1,000. As far as could be judged by the ruins of the tunnel, which it was found necessary to demolish in order to replace it by the tunnel of Prince Torlonia, it had a cross section of 11 9 square yards, and its head is supposed to have been somewhere about 3 feet above the then bottom of the lake. In the construction of this tunnel the Romans sank about forty shafts, twenty-nine between the foot of Mount Salviano and the river Liris, and the remainder between the mountain and the lake, ranging from 57.72 feet to over 400 feet in depth. One of these shafts, which was opened whilst constructing the Torlonia tunnel, was found to be square, each side measuring 14 16 feet, and supported in the middle by strong cross beams dividing the shaft into four equal compartments. The tunnel of Claudius was

6,178 59 yards in length, and it passed through the following soils in its course from its outfall to its head :

Yards.

It will be sufficient here to state that although water is said to have flowed through this channel, its inefficiency soon proved itself, and an accident closed up the tunnel altogether for all practical

purposes.

In 1854, however, Prince Alexander Torlonia decided to carry out the drainage of the lake at his own expense, and he entrusted its execution to M. de Montricher, who was assisted by M. Henri Bermont and M. Alexander Brisse.

In determining the section to be given to the Torlonia tunnel, the conditions of possible rainfall and the capacity of the Liris to receive the discharge were considered. On the former point much uncertainty existed, but M. de Montricher came to the conclusion that under no circumstance should a volume of water greater than 11,000 gallons per second be discharged into the Liris, and this quantity was also found to agree with that of the supply of the lake during a hypothetical rising of 5 feet 10 inches in two months. M. de Montricher, therefore, resolved upon a tunnel having a cross section of 216 square feet and a general slope of 1 in 1,000, and following generally the Roman tunnel which might thus be utilised as a headway.

The new tunnel is egg-shaped in section, truncated at its small base, and resting on an invert 9.3 feet in span, with a versed sine of 9.6 inches. The greater axis measures 19 feet from the bottom of the invert to the crown of the arch; the lesser one, 13.1 feet at a height of 12 feet above the bottom of the invert, which gives a profile having an area of 211 square feet. The slope is generally 1 in 1,000, and with a depth of water of 17.25 feet upon the invert, the discharge is 11,000 gallons per second. The datum point was fixed at the outfall of the tunnel, 33 feet above the bed of the river, and 81 feet below the Roman invert at that place. The deepest part of the lake was at this time 48 feet above datum, and at a distance of 11 miles from the bench-mark at the outfall. The surface of [1877-78. N.S.]

2 B

the lake was 98 feet above datum, and its depth 50 feet. The invert of the Torlonia tunnel, at its outfall on the Liris, was placed 6 feet above datum, or 2 65 feet lower than the Roman tunnel at that spot. Thence it is carried at a slope of 2 in 1,000 for the first 393 yards, and at 1 in 1,000 for the rest of its length.

The works were commenced by the construction of a dam, to cut off the waters of the lake from the head of the Roman tunnel. This dam was formed by two parallel arms, 240 yards distant from each other, and connected by a curve of 120 yards radius, its total length being 1,640 yards. Its top was protected by a strong stone revetment, and for further protection an inner dam was also constructed, with a space between the two of about 32 acres. About 196,200 cubic yards of earth and 39,300 cubic yards of stone were employed in the construction of these works. The tunnel was commenced at the outfall towards the end of 1855, the greater part of it being constructed with hewn stone, brickwork only being occasionally introduced. Considerable difficulties were experienced during the progress of the work, owing to the quantity of water met with in the shafts, the workmen having sometimes to labour in water and mud up to their waists. As soon as the first 5,084 yards of tunnel had been completed, a communication was opened with the old Roman tunnel, into which the waters of the lake were directed, in order to reduce their head before completing the works. This preliminary draining lasted four hundred and seventeen days, and reduced the level of the lake by 14 feet, after which the tunnel was continued as far as the head of the Roman work, when a second draining of the lake was commenced, a canal being cut to direct the waters of the lake to the tunnel. The surface of the lake, at the completion of this draining, was lowered another 25 feet, its depth reduced to 18 feet, and its area to 23,230 acres. The tunnel was completed in November 1869 to a length of 6,887 yards, of which 2,813 yards were excavated through the compact rock without revetment, 344 yards through pudding stone and lined with brick, and 3,729 yards through clay, detached rocks, &c., and lined with strong masonry of hewn stone. For its construction twenty-eight shafts were sunk or repaired, having an aggregate length of 1,560 yards, and two inclined galleries, together 568 yards long. The deepest of the shafts made use of for removing the excavated material was 154 feet, and the shallowest 55.44 feet. Twelve of the twenty-eight shafts were above 279 feet in depth.

For the last 22 yards of its length the tunnel gradually widens, and at its mouth is divided by a cutwater into two small tunnels, each of which is fitted with a sluice gate; and 7 feet advance of this is the real entrance, consisting of a semicircular in arch springing from vertical side walls 197 feet apart, and in front of this again is a regulating basin. regulating basin. In order to drain the lower part of the lake, a canal was excavated leading to the head of the tunnel, having the same capacity as the tunnel itself, and a slope of 1 in 6,959, its bottom width being 49.21 feet, and its

sides having a batter of 45°. This canal, 8 miles in length, was formed by dredging, effected whilst the waters were still being drained off from the lake. The further works undertaken to complete the reclamation of land consisted of 130 miles of roads, 62 miles of canals and drains (inclusive of the main canal, but exclusive of the tunnel), and 4021 miles of ditches, and the land reclaimed amounts to 35,012 acres.

The total aggregate cost of this work to Prince Torlonia was 43,137,208 francs, or about £1,800,000. Of this a little over £1,000,000 sterling was the cost of the tunnel, canal, and drainage works generally; £600,000 for compensations, roads, bridges, drains, and incidental expenses, including 5 per cent. interest on capital during construction of the works, and something under £200,000 for preliminary expenses, purchase of concession, contribution towards improving the channel of the river Liris, and other minor incidental charges.

It is calculated that, by the increase in value of land previously cultivated, the drainage of Lake Fucino has added £160,000 to the wealth of the proprietors along its shores, which it is expected, in the course of a few years, will still further increase. In addition to this there remains the 35,012 acres reclaimed from the lake, the proprietary of which is vested in Prince Torlonia in return for his expenditure in the construction of the works.

F. C. D.

The Port of Havre.1 By Q. DE ROCHEMONT, Assoc. Inst. C.E. (Report made to the Congress of the French Association for the Advancement of Science, Havre, 1877.)

The port of Havre, the second in importance among the ports of France, is distinguished by special features. Situated on the shores of the Atlantic, it is subject to high tides, which are attended by a remarkable phenomenon that is displayed along the entire level from Cherbourg to Dieppe. This is the étale, or slack water; in virtue of which the high tide remains stationary, not for the usual brief period, but sometimes even for hours. extraordinary advantage is thus secured to Havre over other French ports opening on the ocean; as the period during which vessels can enter or leave the basins is thus prolonged.

An

Havre is commonly called the Port of Paris, from which city it is distant 141 miles. The two cities are connected both by railway and by the navigable river Seine. The utility of the latter as a means of communication, however, is much impaired by the sandbanks and other difficulties of the navigation. Not only large ships,

1 The first portion of this Paper is taken from an article in the Giornale del Genio civile, vol. xv., p. 250, “On the Harbours of Havre and Marseilles," by G. Balzaretti.