FOUNTAIN. By this term is desig nated any natural or artificial apparatus by means of which water springs up. In natural fountains the aseensional effort is produced by the hydrostatic pressure of the water itself; in artificial fountains it is produced either by the same pres sure, or by that of compressed air, or sometimes by machinery.
The theory of natural fountains is ex tremely simple : it depends on the well known property of fluids, which when inclosed in tubes or vessels communica ting with each other, the fluid rises to the same level in all of the tubes: the pressure on the sides of the tube at any point being equal to the height of the vertical column above the tube.
Now it is precisely on this principle that all natural fountains are explained. The rain which falls from the atmosphere is absorbed in three different ways. One part of it collects in rills on the surface of the ground ; these unite in streams or rivulets, which flowing into one another form rivers, and thus it is conveyed to the ocean. A second part is taken up in giving humidity to the soil, from which it is returned to the atmosphere by eva poration. A third portion descends into the earth, through soils of a spongy or porous nature, or through crevices and in terstices in the strata, until it meets, fre quently at a very considerable depth, with strata through which it cannot penetrate, and is then collected in subterraneous reservoirs. When confined in this man
ner it is subject to the pressure of the water which fills the channels through which it has descended; and when this pressure is sufficient to overcome the re sistance of the superincumbent mass of earth, the water breaks the artificial stra ta, and gushes forth in a spring. But if the strength of the superincumbent ma terials exceed the hydrostatic pressure, the water will remain stored up as it were in the subterraneous reservoir. Now if the ground above such a reser voir, or any channel communicating with it, be perforated, the water, having free access to the opening, will rise in it till it attains the level of the highest part of the channels from which it is supplied. If this level is above the surface of the ground, the water will have a tendency to rise ; and when the ascensional force is considerable, it may by proper means be formed into a fountain. That snbter raneous reservoirs formed in this man ner exist in great abundance, and at great depths under the surface, we have suffi cient evidence in the facility with which water may be obtained in almost all countries from Artesian Wells.