devised methods of raising water, automatic
contrivances, and amusing things of many kinds, including among them the
construction of water clocks. He began by making an orifice in a piece
of gold, or by perforating a gem, because these substances are not worn
by the action of water, and do not collect dirt so as to get stopped up.

5. A regular flow of water through the orifice raises an inverted bowl,
called by mechanicians the "cork" or "drum." To this are attached a rack
and a revolving drum, both fitted with teeth at regular intervals. These
teeth, acting upon one another, induce a measured revolution and
movement. Other racks and other drums, similarly toothed and subject to
the same motion, give rise by their revolution to various kinds of
motions, by which figures are moved, cones revolve, pebbles or eggs
fall, trumpets sound, and other incidental effects take place.

6. The hours are marked in these clocks on a column or a pilaster, and a
figure emerging from the bottom points to them with a rod throughout the
whole day. Their decrease or increase in length with the different days
and months, must be adjusted by inserting or withdrawing wedges. The
shutoffs for regulating the water are constructed as follows. Two cones
are made, one solid and the other hollow, turned on a lathe so that one
will go into the other and fit it perfectly. A rod is used to loosen or
to bring them together, thus causing the water to flow rapidly or slowly
into the vessels. According to these rules, and by this mechanism, water
clocks may be constructed for use in winter.

7. But if it proves that the shortening or lengthening of the day is
not in agreement with the insertion and removal of the wedges, because
the wedges may very often cause errors, the following arrangement will
have to be made. Let the hours be marked off transversely on the column
from the analemma, and let the lines of the months also be marked upon
the column. Then let the column be made to revolve, in such a way that,
as it turns continuously towards the figure and the rod with which the
emerging figure points to the hours, it may make the hours short or long
according to the respective months.

8. There is also another kind of winter dial, called the Anaphoric and
constructed in the following way. The hours, indicated by bronze rods in
accordance with the figure of the analemma, radiate from a centre on the
face. Circles are described upon it, marking the limi