FOUNTAIN OF HERO. An ingeni ous hydraulic machine, ascribed to Hero of Alexandria, who lived 150 years B. C. Its principle depends on the transmis sion of the pressure sustained by a body of water in one vessel to that in another by means of the elasticity of air. The essential parts of the fountain consist of two close vessels, A and B. The one placed somewhat above the other, and connected by a frame ;• and having a let pipe in the centre, its lower end reaching near the bottom of A. A pipe passes down from A to near the bottom of B: another pipe is connected with B and passes up to near the top of A. This pipe conducts air from B to A. When water is poured into A it runs down the pipe into B; this drives the air up the pipe into the upper part of A, which presses on the surface of the water there and compels it to pass up the jet-pipe and issue out as a fountain, the height of which is equal to the difference of the levels of the water in C and B: the wa ter will, according to the theory, spout to a height above its level in A equal to that distance.
The second figure represents the foun tain of Hero in another form. An appa ratus of this kind is used to drain the Hungarian mines at Schemnitz.
Artificial fountains are also produced by means of the elasticity of heated air, or air condensed by some other means. Two different forms are used for this purpose. The first consists of two close vessels of tin, placed one above the other; the lower one being of considerable size : the upper, famished with a tube or jet, which reaches to near the bottom of the vessel. On applying the heat of a lamp to the lower vessel, the air within it expands and forcing its way through the open tube is com pressed at the top of the vessel, and thus by its pressure forces the water in that vessel through K, L, forming a small jet at K. This apparatus being generally constructed in the form of a temple, produces a very pleasing effect.