69. A Siphon fixed in a Vessel from which the Discharge shall cease at will.
There are certain siphons which, when placed in vessels, flow until the vessels are emptied, or the surface of the water has sunk to the level of the outer orifice of the siphon. Let it be required that the discharge shall suddenly cease whenever we wish. A B (fig. 69), is a vessel containing a siphon, C D E, the inner leg of which is bent upwards as at C F G. Let a vertical rod H K be fixed, on which another, L M, works as a lever-beam: from L M extends another rod, M N, moving on a pivot, and provided at the extremity N with a vessel large enough to encircle the bent portion of the siphon F G. On the rod L M suspend a weight at L, so that the encircling vessel is raised above the upward bend of the siphon, and the siphon flows. When we wish the discharge to cease, we have only to remove the weight at L, and the vessel at N will descend and encircle the bend G C, so that the siphon will cease to flow. If it is desired that the stream should continue, we must again suspend the weight.