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month. Wherefore, as the sun passing through the 
signs, lengthens and shortens the days and hours, so the 
index of the dial, entering by the points opposite the 
centre round which the wheel turns, by its daily motions. 
sometimes in greater, at other times in less periods, will 
pass through the limits of the months and days. The 
management of the water, and its equable flow, is thus 
regulated. Inside, behind the face of the dial, a cister 
is placed, into which the water is conveyed by a pipe. In 
its bottom is a hole, at whose side is fixed a brazen tym- 
panum, with a hole in it, through which the water in the 
cistern may pass into it. Within this is inclosed a lesser 
tympanum attached to the greater, with male and female 
joints rounded, so that the lesser tympanum turning 
within the greater, similar to a stopple, fits closely, 
though it moves easily. Moreover, on the lip of the 
greater tympanum are three hundred and sixty-five 
points, at equal distances. On the circumference of 
the smaller tympanum a tongue is fixed, whose tip 
points to the marks. In this smaller tympanum a 
proportionable hole is made, through which the water 
passes into the tympanum, and serves the work. On 
the lip of the large tympanum, which is fixed, are 
the figures of the celestial signs; above, is the figure 
of Cancer, and opposite to it, below, that of Capri- 
cornus. On the right of the spectator is Libra, on 
his left Aries. All the other signs are arranged in the 
spaces between these, as they are seen in the heavens. 
Thus, when the sun is in the portion of the circle 
occupied by Capricornus, the tongue stands in that 
part of the larger tympanum where Capricornus is 
placed, touching a different point every day: and as 
it then vertically bears the great weight of the run- 
ning water, this passes with great velocity through 
the hole into the vase, which, receiving it, and being 
soon filled, diminishes and contracts the lengths of 
the days and hours. When, by the diurnal revolu¬