There is another way in which, on lighting a fire, the doors will open.
As before, let a small temple stand upon a base, A B C D (fig. 38), on
which is an altar, E. Let a tube, F G H, pass through the altar and
be attached to a leathern bag, K, perfectly air-tight : beneath this let
a small weight, L, hang, from which a chain is attached across a pulley
to the chains round the hinges, so that, when the bag is folded
together, the weight L preponderates and shuts the doors, and when fire
is placed on the altar they are opened. For, as before, the air in the
altar growing hot, and expanding, will pass through the tube F G H into
the bag, and raise it up with the weight L; and then the doors will be
opened. The doors will either open of themselves, as the doors of baths
shut spontaneously, or they may have a counterbalancing weight to open
them. When the sacrifice is extinguished, and the air which has entered
the bag passes out, the weight, descending with the bag, will tighten
the chains and close the doors.