the level of the rises to more than 0.005 above the regulation reserve. The fetching (amorcement) is then effected in the following manner: As soon as the water rises above the regulation reserve, it flows over the lower lip of the fetching tube; if this elevation attains 0.005 the entrance orifice of the fetching tube is submerged, and from that time the air contained in the fetching tube, in the siphon, and in the upper tube ceases to be in communication with the atmosphere. Then the water, in overflowing, draws the air from the small tubes and exhausts that of the siphon, and there ensues a diminution of pressure in the interior of the apparatus, the water ascends into the siphon, the fetching takes place, and finally the siphon works with increasing speed and discharge. But another phenomenon prevents the pressure from indefinitely diminishing, and the delivery from indefinitely augmenting. The increasing velocity of the water entering the fetching tube creates, near its head, a partial depression in the plane of the fluid; this depression deepens in proportion to the augmentation of speed, and at last reaches and uncovers the upper lip of the orifice, thereby causing the admission of a certain quantity of air into the apparatus, a consequent increase of interior pressure, and a diminution of speed. The same facts being successively produced, there results from these two opposing tendencies a series of oscillations corresponding to the shutting and liberating the upper lip of the fetching tube. This state of agitation soon ceases, and a steady movement is established, during which there is a simultaneous issue of water and air. When the rising of the water ceases the level of the reservoir lowers, and the same phenomena are produced in an inverse direction; the siphon action stops, and the flow is arrested when the plane of the water returns it to its normal height. A few millimeters of elevation in the plane of the water above the fetching tube suffice to cause a marked increase of speed. The air ceases to enter and the water escapes from the filled tube before this elevation has attained the permissible limit, 0.05. The discharge is then 0.60 per second, a quantity greater than the maximum delivery of the risings. In order to exercise complete control over the apparatus, the head of the fetching tube has been disposed in such a manner that it can be raised or lowered in a single piece, by the aid of a regulating screw, the impermeability of the communications being assured by free dilata. tion joints. In addition, a small vertical iron valve gate has been placed in the head of the fetching tube, and it can move round a vertical axis, without ceasing to fit closely to the interior of the two lips, which allows the entrance aperture and consequently the discharge to be varied. The regulating is effected once for all, and the apparatus afterwards works automatically and requires no supervision. The apparatus is double, and consists of two siphons, each of which is furnished with its own fetching tube, with tube of communication. Thus each siphon forms a complete system, capable of working by itself while the other may require to be examined, repaired, or regulated. The idea of employing fixed siphons as weirs for the regulation of a reserve was proposed by M. Girard and applied to the Southern Canal; but large siphons have been employed there, which required considerable variations in the level of the reserve, to put them in motion or to stop them. The peculiar conditions existing at Mettersheim and the very restrained limit permissible. 0.05, led M. Hirsch, engineer "des Ponts et Chaussées," to invent the special system of fetching tubes, which has completely fulfilled the purpose for which it was intended. Water was let into the reservoir in December, 1866, and the siphons were put in action, for the first time, on the 12th January following. SAINT LOUIS CANAL. IMPROVEMENT OF THE EMBOUCHURES OF THE RHONE. (Drawings.) Numerous attempts have been made to lower the bar of the Rhone, where this river discharges its waters into the Mediterranean, but hitherto they have resulted in failure. It was therefore decided to open a direct communication between the Gulf of Foz and the deep part of the river, above the bar, by means of a canal designated the "Saint Louis Canal." This canal begins on the left bank of the Rhone, at the commence. ment of the dike constructed in 1856, for the enbankment of the Bras de l'Est (Eastern Arm), at a distance of 600 meters below the Tour Saint Louis, and taking a straight line from west to east, it terminates in the Gulf of Foz, opposite the port of Bouc. At the Rhone end it is closed by a lock, while at the sea it discharges into a port formed by two jetties. On the canal side of the lock a basin has been excavated to enable vessels to turn round, in order to pass from the lock into the canal, and vice versa. The Saint Louis Canal having been established as a substitute for the natural embouchure of the Rhone, it was necessary to create a depth of water exceeding that of the river itself below the port of Arles. Between Arles and Saint Louis the depth of water is scarcely 2 meters, and even with the improvements now being made it does not appear probable that more than 4 meters will ever be obtained, in consequence of the reefs of hard pudding-stone encountered at certain points in the bed of the river. A depth of 4 meters was therefore considered sufficient for the mouth of the canal. But the idea presented itself that, the entrance of the Rhone once rendered practicable, the river traffic would immediately take such a development that it would be absolutely necessary to secure the possibility of putting it into communication with the maritime navigation. For this reason, the Gov. ernment decided to give a depth of 5 meters to the Saint Louis Canal. For a maritime channel of such dimensions, it was essential to create a port on the Rhone capable of receiving vessels coming from the sea by the canal. This port was formed at Saint Louis itself; the basin was enlarged sufficiently to admit of the necessary maneuvers of vessels; quays were built, and at the present moment others are in course of construction on the Rhone, just above the outlet of the canal. The canal properly so called is 3,330 meters in length from its entrance into the basin at one end to the sea-shore at the other. It is 6 meters in depth below the level of low tides. The width at the bottom is 30 meters, and at the level of low tides 63 meters. On each side of the canal a towing path has been formed, 12 meters in breadth, with a level of 2 meters above the water. Along the whole length of the towing paths the earth excavated from the canal was put in depots or spoil-banks, and these have been kept 2m.50 above water level in such a manner as to be above the highest level of the waters of the Rhone, and to protect the canal in case of inundation. The basin is 400 meters in length by 300 in width. Quay walls have been built on three sides, and the length finished up to the present time is 850 meters. This length will attain 1,100 meters when the walls in course of construction are terminated on the western, northern, and eastern sides. The capping of the quays is established 2.50 above water level, and the earth platforms behind are made flush to the same height. The works of the canal and basin were executed dry, by the aid of two coffer-dams-one at the sea end, the other in the excavations for the lock. A third coffer-dam was formed about half way between the two, in order to provide against the contingency of either of the end dams giving way. They were made partly with the natural soil and partly with the clayey ground taken from the cuttings. The draining was accomplished by means of rotary pumps (Neut, and Dumont), worked by a portable engine. There was a pumping shaft for each of the divisions into which the canal and basin were separated by the center coffer-dam, in which last auxiliary pumping machinery was established. Each shaft was furnished with two rotary pumps, and two portable engines of 8 to 10 horse-power. The port is formed by two jetties, of which the southern one is paral lel to the axis of the canal at a distance of 48m.25 from the axis; it advances as far as the natural bottom of 6m.50, and is 1,746m.20 in length. The other commences 1,350 meters to the north of the canal; it has only advanced as far as the natural bottom of 3.25 and is at present but 500 meters in length. Being perpendicular to the direction of the bank, it tends towards the wing wall of the northern jetty in such a manner that if the two jetties should be carried out on a straight line |
