60 PHYSICS. 
passes through a small opening in the bottom of the vessel p into the lower 
receptacle, the inferior opening of the tube ¢ again becomes free, and the 
discharge through 7, 7 begins afresh. 
Hero’s fountain is essentially nothing else than a self-acting Hero’s ball, 
in which the compression of the air which drives out the water is produced 
by means of a column of water. Sig. 63 represents the apparatus in its 
simplest form, which, if not blown in one piece, may consist of vessels 
connected together by glass tubes. To use it, the upper vessel, c, is filled with 
water through d, until it stands nearly up to the termination of the tube b. 
Filling the vessel above a with water, the water descending in a compresses 
a column of air in b, whose elasticity and pressure upon the surface of 
the water in c¢, force out the water through d. Fig. 64 represents a some- 
what more complicated form of this apparatus, where the tube z answers to 
the tube a in fig. 63, and y to the tube 0 ; the vessel z occupies the place of the 
lower ball, and the upper vessel that of the ball at c; and at a is the 
discharge pipe, which reaches nearly to the bottom of the vessel. 
A pump (suction pump) in its simplest form is a tube of uniform diameter 
within, open at both ends, and the lower dipping into water. In this tube 
may be moved up and down a well-fitting and air-tight piston attached to a 
rod. Supposing at first the piston to stand at or near the surtace of the 
water, and that it be elevated by means of the rod, then the water, by the 
pressure of the air on the surrounding liquid, will be forced into the pump, and 
ascend to a height of not more than 32 feet. If the water is to be not only 
raised but turned into a receiver, its return must be prevented, and some 
provision made for getting it above the piston. The lower extremity of the 
pump tube in this case must not be open, but must have a bottom provided 
with a valve opening upwards; also with a suction tube dipping into the 
water where it may be closed by a strainer. The piston also must have a 
valve opening upwards. On raising the piston, the water is forced by 
atmospheric pressure through the lower valve into the pump tube, the valve 
in the piston remaining closed; on depressing the piston, its valve is opened 
by the pressure of the water, which then rushes through it and occupies a 
place above, the return of the water through the lower valve being prevented 
by its closing. By repeated elevations and depressions of the piston, the 
water is at length lifted to the level of the top of the tube, or to an orifice in 
the side where it can escape. If the water is not to flow directly from the 
pump tube, but into some other place, or if it is to be discharged with great 
force, or carried to a great height, the forcing-pump must be employed, as 
represented in pl. 17, fig. 34. It consists of a pump-stock or tube in which 
is a massive cylindrical piston, F, moving up and down, passing air-tight 
through a stuffing box, EH, and a grease box, D, but without touching the 
pump tube itself, which therefore need not be perfectly cylindrical in its 
box. 
Upon the suction tube, C,is placed the valve lid, f, with the valves 3, 7, 
through which, on raising the piston, the water passes into the cylinder ; on 
depressing the piston, the water is driven into the tube B, after forcing open 
its valve, d. On raising the piston again, the valve d falls, and the valves 2, 1, 
234 
