[Illustration: Diagram of apparatus as described in text]
To construct an altar such that, when a fire is raised on it, figures
at the side shall offer libations. Let there be a pedestal, A B C
D, (fig. 11) on which the figures stand, and also an altar, E F
G, perfectly air-tight. The pedestal must also be air-tight, and
communicate with the altar at G. Through the pedestal insert the tube H
K L, reaching nearly to the bottom at L, and communicating at H with a
bowl held by one of the figures. Pour liquid into the pedestal through
a hole, M, which must afterwards be closed. Now if a fire be lighted
on the altar E F G, the air within it, being rarefied, will descend
into the pedestal, and exert pressure on the liquid it contains, which,
having no other way of retreat, will pass through the tube H K L into
the bowl. Thus the figures will pour a libation, and will not cease so
long as the fire remains on the altar. When the fire is extinguished,
the libation ceases; and as often as the fire is kindled the same
will be repeated. The pipe through which the heat is to pass should
be broader towards the middle, for it is requisite that the heat, or
rather the vapour from it, passing into a broader space, should expand
and act with greater force.
12. _A Vessel from which the contents flow when filled to a certain
height._
[Illustration: Diagram of apparatus as described in text]
There are some vessels which emit no stream unless they are filled; but
when filled discharge all the liquid they contain. They are made as
follows: Let A B C D (fig. 12) be a vessel open at the top, and through
its bottom pass a tube, either an inclosed diabetes as E F G, or a bent
siphon G H K. When the vessel A B C D is filled, and the water runs
over, a discharge will begin through the diabetes, and continue till
the vessel is empty, if the interior opening of the diabetes is so near
the bottom of the vessel as only to leave a passage for the water.
13. _Two Vessels from which the contents flow, by a Liquid being poured
into one only._
[Illustration: Diagram of apparatus as described in text]
If two vessels, both of them having visible outlets, stand upon a
pedestal, and one of them be filled with wine, the other remaining
empty, the wine shall not flow out until the empty vessel be filled
with water; and then a discharge shall begin, of wine from one, and of
water from the other, until both are empty. Such vessels are called
_harmonious goblets_. Let A B C D (fig. 13) be the pedestal on which
the vessels, E and F, stand. In each of them place a bent siphon, G H K
in E, and L M N in F, and let the outer extremities of the siphons be
shaped like water-pipes. At the bend the siphons must approach nearly
to the mouths of the vessels. Let another bent tube, X O P R, passing
through the pedestal, connect the two vessels, the extremities of
which, X and R, must reach as high as the bend of the siphons. Now pour
wine into one vessel, taking care that it does not mount higher than
the bend of the siphon at H. Up to this point the wine will not flow
out, as there is nothing to originate a discharge through the siphon.
But if we pour water into the vessel F, until its surface mounts above
the bend of the siphon at M, then the water will descend and pass
through the pipe X O P R into the other vessel. Thus a discharge is
occasioned of the wine also, and both vessels will continue to run the
one with wine, the other with water, until both are emptied.