nferior to the original....

_De natura deorum_, II, xxxiv-xxxv (88),
Yonge's translation.

In spite of the lack of sufficient technical details in any case, these
mechanized globe models, with or without geared planetary indicators
(which would make them highly complex machines), bear a striking
resemblance to the earliest Chinese device described by Chang Heng. One
must not reject the possibility that transmission from Greece or Rome
could have reached the East by the beginning of the 2nd century, A.D.,
when he was working. It is an interesting question, but even if such
contact actually occurred, very soon afterwards, as we shall see, the
western and eastern lines of evolution parted company and evolved so far
as can be seen, quite independently until at least the 12th century.

The next Hellenistic source of which we must take note is a fragmentary
and almost unintelligible chapter in the works of Hero of Alexandria.
Alone and unconnected with his other chapters this describes a model
which seems to be static, in direct contrast to all other devices which
move by pneumatic and hydrostatic pressures; it may well be conjectured
that in its original form this chapter described a mechanized rather
than a static globe:

The World represented in the Centre of the Universe: The
construction of a transparent globe containing air and
liquid, and also of a smaller globe, in the centre, in
imitation of the World. Two hemispheres of glass are made;
one of them is covered with a plate of bronze, in the
middle of which is a round hole. To fit this hole a light
ball, of small size, is constructed, and thrown into the
water contained in the other hemisphere: the covered
hemisphere is next applied to this, and, a certain
quantity of the liquid having been removed from the water,
the intermediate space will contain the ball; thus by the
application of the second hemisphere what was proposed is
accomplished.

_Pneumatics_, XLVI, Woodcroft's translation.

It will be noted that these earliest literary references are concerned
with pictorial, 3-dimensional models of the universe, moved perhaps by
hand, perhaps by waterpower; there is no evidence that they contained
complicated trains of gears, and in the absence of this we may incline
to the view that in at least the earliest such models, gearing was not
used.

The next developments were concerned on the one hand with increasing the
mathema