FIG. 1.—A MIRACULOUS VESSEL OF HERON.
“Let Α Β be a vessel containing a quantity of water equal to that which may be demanded, and Γ Δ a tube that puts it in communication with a reservoir, Η Θ, lower down. Near this tube there is fixed a lever, Ε Ζ, from whose extremity, Ε, is suspended a cork float, Κ, and to whose other extremity, Ζ, there is hooked a chain that carries a leaden weight, Ξ.
“The whole should be so arranged that the cork, Κ, which floats on the water, shall close the tube’s orifice; that when the water flows out, the cork, in falling, shall leave such aperture free; and, finally, that when a new supply of water enters, the cork shall rise with it and close the orifice anew. To effect this the cork must be heavier than the leaden weight suspended at Ξ. Now, let Λ Μ be a vessel whose edges should be at the same height as the level of the water in the reservoir when there is no flow through the tube because of the cork float. Again, let Θ Ν be a tube that connects the reservoir with the base of the vessel, Λ Μ.
FIG. 2.—MIRACULOUS VESSEL OF HERON.
“So, then, when we remove water from the vessel, Λ Μ, after it has once been filled, we shall at the same time lower the level of the water in the reservoir, and the cork, in falling, will open the tube. The water thereupon running into the lower reservoir, and from thence into the external vessel, will cause the cork to rise and the flow to cease, and this will occur every time that we remove water from the tazza.”
There were, also, vessels which discharged but a certain definite quantity of the liquid that they contained. We have already described one of these, but here is another that is more complicated, wherein the quantity of liquid that it measures out may be caused to vary in the same vessel.
A vessel containing wine, and provided with a spout, being placed upon a pedestal, to cause the spout, by the simple moving of a weight, to allow a given quantity of wine to flow; now, for example, half a cotyle (0.13 liter), and now a whole cotyle; or, briefly, any quantity that may be desired.
“Let Α Β be the vessel into which the wine is to be put ([Fig. 2]). Near its bottom there is a spout, Δ. Its neck is closed by a partition, Ε Ζ, through which passes a tube that runs to the bottom, but leaving, however, sufficient space for the passage of the water. Let Κ Λ Μ Ν be the pedestal upon which the vessel stands, and Ξ Ο another tube that reaches as far as the partition and enters the pedestal. In the latter there is sufficient water to stop up the orifice of the tube, Ξ Ο. Finally, let Π Ρ be a lever, half of which is in the interior of the pedestal and the other half external to it, and which pivots on the point Σ, and carries suspended from its extremity, Π, a clepsydra having an aperture, Τ, in the bottom.