Page:Encyclopædia Britannica, Ninth Edition, v. 2.djvu/240

Rh 222 AQUEDUCT constructed, which excited some attention, as being an improvement on the method of conducting water by aqueduct bridges. &quot; The souterasi,&quot; says Andreossy, &quot; are masses of masonry, having generally the form of a truncated pyramid or an Egyptian obelisk. To form a conduit with souterasi, we choose sources of water, the level of which is several feet higher than the reservoir by which it is to be distributed over the city. We bring the water from its sources in subterranean canals, slightly declining until we come to the borders of a valley or broken ground. &quot;We there raise on each side a souterasi, to which we adapt vertically leaden pipes of determinate diameters, placed parallel to the two opposite sides of the building. These pipes are disjoined at the upper part of the obelisk, which forms a sort of basin, with which the pipes are connected. The one permits the water to rise to the level from whence it had descended ; by the other, the water descends from this level to the foot of the souterasi, where it enters another canal under ground, which conducts it to a second and to a third souterasi, where it rises and again descends, as at the last station. Here a reservoir receives it and distributes it in different directions by orifices of which the discharge is known.&quot; Again he says, &quot; it requires but little attention to perceive that this system of conducting tubes is nothing but a series of syphons open at their upper part, and communicating with each other. The expense of a conduit by souterasi is estimated at only one- fifth of that of an aqueduct with arcades.&quot; There seems to be really no advantage in these pyramids, further than as they serve the- purpose of discharging the air which collects in the pipes. They are in themselves an evident obstruction, and the water would flow more freely without any interruption of the kind. In regard to the leaden pipes, again, they would have required, with so little head pressure as is stated, to be used of very extra ordinary dimensions to pass the same quantity of water as was discharged along the arched conduits. There is some thing, therefore, which would require explanation in the account Anclreossy gives of these pyramids, if, indeed, he did not misunderstand the nature of them. The other principal source from which Constantinople is supplied, is from the high grounds 6 or 8 miles west of the town, from which it is conducted by conduits and arches, in the same manner as the others. The supply drawn from all these sources, as detailed by Andreossy, amounted to 400,000 cubic feet per day. The charge of the water-works at Constantinople belongs to a body of 300 Turks and 100 Albanese Greeks, who form almost an hereditary profession. In ancient Egypt and Babylonia a different problem of water supply was presented, both countries being flat and traversed by great rivers, from which they were subject to regular inundations. Hence canals with large basins took the place of the aqueducts of Greece and Rome, and the stupendous scale on which in Egypt the waters of the Nile, and in Babylonia the waters of the Tigris and Euphrates, were utilised, was a marvel to ancient travellers. In France various aqueducts have been formed after the manner of the Romans. The most remarkable are those constructed in the reign of Louis XIV., at vast expense, for conducting water from Marly to Versailles. The famous aqueduct bridge of Maintenon, which was erected for con veying the waters of the river Eure to Versailles, is without doubt, in point of magnitude and height, the most magni ficent structure of the kind in the world. In Plate IV. a view is given of a portion of this work, on the same scale as the others there represented. Had the whole been delineated on the same scale, it would have extended to four times the breadth of the plate. It extends about 4400 feet in length, that is, about five-sixths of a mile, is upwards of 200 feet in height, and con tains 242 arcades, each divided into three rows, forming in all 726 arches about 50 feet span. Of the subterranean aqueducts in France the finest is that of Arcueil, which serves to conduct water to that village. It is 44,300 feet in length, or upwards of 8 miles, extending from the valley of Arcueil to the castle at the gate of St Jaques, all built of hewn stone. It is about 6 feet in height, and has on each side a foot-path 18 inches wide; it has a declivity of 1 foot in 1300. Another aqueduct of this kind is that of Rocquancourt, part of the system which brings water to Versailles; it is 11,760 feet in length, or upwards of 2 miles, and has a declivity in its whole course of only 3 feet. In some parts of its course it was necessary to make excavations 80 or 90 feet deep, which rendered the execution very difficult. The great waterworks that supply the city of Marseilles with the water of the Durance, by a canal about 60 miles in length, are among the boldest undertakings of the kind in modern times. This canal, begun in 1839, and com pleted in 1847, is conveyed through three chains of lime stone mountains by forty-five tunnels, forming an aggregate length of 8 1 miles, and across numerous valleys by aque ducts ; the largest of which, the Aqueduct of Roquefavour, over the ravine of the River Arc, about 5 miles from Aix, surpasses in size and altitude the ancient Pont du Gard. The immense volume of water, which passes at the rate of 198,000 gallons per minute, is carried across as in the old Roman aqueducts by a channel of masonwork. The height of this aqueduct is 262 feet, and its length 1287. One other aqueduct of modern construction is worthy of notice. In those parts of British India where the fall of rain is scanty and uncertain, recourse is had to artificial irrigation, and the waters of many of the rivers of the country have been rendered available for this purpose by means of public works constructed by the Government. Of these the most important is the Ganges Canal, which traverses the North- Western Provinces of Bengal, and dis tributes over their vast area nearly the whole volume of the waters of the Ganges. The canal begins at the point where the river issues from the mountains, and enters the plains of Bengal. About 20 miles from its source, the line of the canal crosses the valley of the Solani river, and the works for effecting the transit are designed on a scale worthy of the undertaking. The valley is between 2 and 3 miles in width. An earthen embankment is carried across, raised on an average between 1 G and 1 7 feet above the surrounding country, and having a width of 350 feet at its base, and 290 feet in the upper part. This embankment forms the bed of the canal, which is protected by banks 12 feet in depth, and 30 feet wide at the top. To preserve these banks from the effects of the action of the water, lines of masonry formed into steps extend on each side throughout their entire length. The Solani river is crossed by an aqueduct 920 feet long, having side walls 8 feet thick and 12 deep, the depth of the water being 10 feet. The water of the canal passes through two separate channels. That of the River Solani flows under fifteen arches, having a span of 50 feet each, constructed in the most substantial manner, and springing from piers resting on blocks of masonry sunk into the bed of the river. The cost of the aqueduct was upwards of XI 60,000. In grandeur of design, solidity of construction, and, above all, in extensive utility, it may challenge competition with any similar work in the world. Within the last century, the invention and improvement of the manufacture of cast iron has completely changed the mode of conducting water into cities, by the introduction of cast-iron pipes instead of the stone conduits of former times. These pipes can now be formed of almost any