h their throats from a tank below. The owl
is made to turn by a mechanism similar to that which manipulates the
temple doors. The pressure is supplied merely by a stream of running
water, and the periodical silence of the birds is due to the fact that
this pressure is relieved through the automatic siphoning off of the
water when it reaches a certain height. The action of the siphon, it may
be added, is correctly explained by Hero as due to the greater weight of
the water in the longer arm of the bent tube. As before mentioned, the
siphon is repeatedly used in these mechanisms of Hero. The diagram will
make clear the exact application of it in the present most ingenious
mechanism. We may add that the principle of the whistle was a favorite
one of Hero. By the aid of a similar mechanism he brought about the
blowing of trumpets when the temple doors were opened, a phenomenon
which must greatly have enhanced the mystification. It is possible that
this principle was utilized also in connection with statues to produce
seemingly supernatural effects. This may be the explanation of the
tradition of the speaking statue in the temple of Ammon at Thebes.

{illustration caption = DEVICE FOR CAUSING THE DOORS OF THE TEMPLE TO
OPEN WHEN THE FIRE ON THE ALTAR IS LIGHTED (Air heated in the altar F
drives water from the closed receptacle H through the tube KL into the
bucket M, which descends through gravity, thus opening the doors. When
the altar cools, the air contracts, the water is sucked from the bucket,
and the weight and pulley close the doors.)}

{illustration caption = THE STEAM-ENGINE OF HERO (The steam generated in
the receptacle AB passes through the tube EF into the globe, and escapes
through the bent tubes H and K, causing the globe to rotate on the axis
LG.)}

The utilization of the properties of compressed air was not confined,
however, exclusively to mere toys, or to produce miraculous effects. The
same principle was applied to a practical fire-engine, worked by levers
and force-pumps; an apparatus, in short, altogether similar to that
still in use in rural districts. A slightly different application of the
motive power of expanding air is furnished in a very curious toy called
"the dancing figures." In this, air heated in a retort like a miniature
altar is allowed to escape through the sides of two pairs of revolving
arms precisely like those of the ordinary revolving fountain with which
we are accustomed to water