The phenomena presented by springs of water are explained by aupposing that the rain which is absorbed in the earth occasionally finds ita way by small channels to some interior cavity, and from thence by other channels, which may be considered as natural aiplions, to an orifice on a lower level at the surface of the ground. At this orifice it issues in a stream of water, which continues to flow till the surface of the water in the cavity has descended below the tops of the vertical bends in the channels : the water then ceases to flow till the rains again raise the water in the cavity above these bends. But it some. times happens that a spring, without ceasing to flow, discharges periodically greater and smaller quantities of water in given times ; and this is accounted for by supposing the existence of two cavities either unconnected or communicating with one another by small channels. The channels leading from one of these cavities to the point of of are supposed to be below the level of the water in both cavities, so that the water flows through thew continually ; but if the channels from the other have vertical bends, se that they act as siphons, and at the same time these channels carry off the water in them faster than it can flow from the first cavity to the second, it will be only when the water in the latter cavity is above the level of all such bends that a discharge will take place from thence. As the water
in that cavity may only attain the necessary height in consequence of periodical falls of rain, it will follow that corresponding increases in the total quantity of water discharged can only then take place.
For the amusement of young persons, several philosophical toys have been constructed, in which the effects are produced by meals of con cealed siphons. The siphon is sometimes placed within a figure in the middle or on the edge of a cup, and sometimes between its exterior and interior sides. Such are Tantalus's Cup and the Siphon Fountain.