equinoctial rises, and about one degree more, through
which degree the sun moves against the motion of the
firmament in the course of a natural day. Moreover, this
could be done more accurately if an astrolabe were
constructed with a network on which the entire equinoctial
circle was divided up.

[Illustration: Figure 19.--MANUSCRIPT ILLUMINATION OF A MEDIEVAL
WATERCLOCK, showing a partitioned wheel, a weight drive, and a carillion
for striking. From Drover (see footnote 34).]

The text then continues with technical astronomical details of the
slight difference between the rate of rotation of the sun and of the
fixed stars (because of the annual rotation of the sun amongst the
stars) but it gives no indication of any regulatory device. Again it
should be noted, this source comes from France; Robertus, though of
English origin, apparently being then a lecturer either at the
University of Paris or at that of Montpellier. The date of this passage,
1271, has been taken as a _terminus post quem_ for the invention of the
mechanical clock. In the next section we shall describe the text of
Peter Peregrinus, very close to this in place and date, which describes
just such a machine, conflating it with accounts of an armillary sphere,
perpetual motion, and the magnetic compass--so bringing all these
threads together for the first time in Europe.

[Illustration: Figure 20.--ARRANGEMENT FOR TURNING A FIGURE OF AN ANGEL.
It has been alleged that this drawing by Villard represents an
escapement. After Lassus (see footnote 37).]

We have reserved to the last one section of evidence which may or may
not be misleading, the famous notebook of Villard (Wilars) of
Honnecourt, near Cambrai. The album, attributed to the period 1240-1251,
contains many drawings with short annotations, three of which are of
special interest to our investigations.[37] These comprise a steeplelike
structure labeled "cest li masons don orologe" (this is the house of a
clock), a device including a rope, wheel and axle (fig. 20), marked "par
chu fait om un angle tenir son doit ades vers le solel" (by this means
an angel is made to keep his finger directed towards the sun), and a
perpetual motion wheel which we shall reserve for later discussion.

The clock tower, according to Drover, shows no place for a dial but
suggests the use of bells because of its open structure, suitable for
letting out the sound. Moreover, he suggests that the delicacy of th