The latter once empty, the siphon will be unprimed, and will reprime itself a few hours later. The instant of unpriming, and consequently the level of the water remaining in the pond, is fully under the control of the farmer. It suffices, in fact, to form a series of apertures a in the short branch of the siphon, and close them with wooden plugs that are removed according as it is desired that the water shall descend to such or such a level in the reservoir.

As shown in the sections in Figs. 279, 280, the apparatus is constructed in two different forms, but the principle of both is absolutely the same.

The bell siphon (Fig 279) consists of a tube, which is inserted in the sluice hole and is provided at its upper part with a circular water reservoir A. A movable bell, provided with an internal circular diaphragm B, covers the whole and rests upon the tube. It is provided with two small external reservoirs R R' connected by a tube t. The lower reservoir R' communicates with the interior of the bell, through small apertures.

Two bent tubes T T' put the reservoir R in communication with the two chambers as formed in the bell by the diaphragm B. A third tube S below the two others starts from the reservoir R, traverses the bell, and hangs vertically in the interior of the central tube fixed in the sluice.

Fig. 280 represents the second form of the apparatus. It is an ordinary doubly revolving siphon. The general arrangements are the same as those just described. It is to be remarked that the part A of the bent siphon will always remain full of water, like the reservoir A in the bell siphon.

Let us suppose that the pond has just been emptied; the unprimed siphon will be entirely empty, except in the parts A. The water gradually rises in the reservoir, and consequently in the short branch of the siphon, in the leservoir R, through the intermedium of the reservoir-R', and in the 3 tubes T T' S. In measure at the water rises, the air is driven forward until the moment that the siphon is about to operate as a wasts pipe. It thus takes a certain pressure in the chamber a (tube T), on account of the presence of water in the internal reservoir A. In the chamber fl, on the contrary, it remains at the pressure of the atmosphere, since the long branch of the siphon opens in the free air. It is starting from this moment that the automatic priming of an ordinary siphon may take place, if the requisite conditions of discharge be pie-sent, the air confined in the upper parts being carried along by the first jet of the liquid. If such conditions are not fulfilled, there always remains in the upper part of the siphon or of the bell some air that must be got rid of, or the pressure of which it will suffice to diminish sufficiently to produce an abrupt ascending motion of the internal liquid column, and consequently a priming.

Siphon for Intermittent discharge.

Such is the principle to be applied, and the way it is done is as follows: In consequence of the presence of a certain volume of compressed air in the internal chamber a, the velocity of the siphon's flow as a waste pi pels infinitely small, and increases proportionally much more slowly than under ordinary circumstances with the external level of the liquid. It results from this, that whatever be the discharge of t he source, the tube S, placed beneath T and T' will bo very quickly immersed.

Id reality, this tube is merely an auxiliary siphon whose diameter is small enough to allow its priming to be always certain. It will therefore empty the reservoir R almost instantaneously. As, on another hand, the latter can fill itself bat slowly, on account of the small diameter of the tube e, there will occur, in order to fill the vacuum formed, an abrupt draught and a putting in equilibrium (through the tubes T T') of the air occupying the internal chambers aβ . At this very moment, the jet of water issuing from the auxiliary siphon in the central tube, or the long branch of the siphon, causes a suction in the chamber β and establishes in the whole (α β) a pressure sensibly less than that of the atmosphere. Prom this complete rupture of equilibrium between the internal liquid and gaseous strata of the siphon results a sort of ram stroke that effects an automatic priming. From the very beginning, the remaining air is carried along by the liquid, with a considerable velocity, dependent upon the height of the water in the.- pond, which latter rapidly empties until the apparatus is un-primed.

Siphon for intermittent discharge.

The system, with a few slight modifications of detail, is applicable as follows: 1, to the flashing chambers in the sewers of large cities; 2, to the submersion of meadows, and in general to all the problems of irrigation; 3, to the automatic emptying and renewing of the water in garden fountains and in ponds especially set apart for pisciculture; 4, and, finally, to the draining of quarries, mine holes, etc., without machines, provided there be a low point for the flow. {La Nature,)