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SCIENCE 575
the moon's attraction. He discussed spring and neap tides, and,
turning to c
things which we know, who live on the shore ofthe
sea divided by Britain*, he described how the wind could advance
or retard a tide, and enunciated for the first time the inv
portant principle now known as *the establishment ofa port*.
This states that the tides lag behind the moon by definite inter'
vals which may be different at different points on the same
shore, so that tides must be tabulated for each port separately.
Bede wrote: 'Those who live on the same shore as we, but to
the north, see the ebb and flow of the tides well before us,
whereas those to the south see it well after us. In every region
the moon always keeps the rule of association which she has
accepted once and for all/ On the basis ofthis, Bede suggested
that the tides at any port could be predicted by means of the
nineteen-year cycle, which he substituted for *s Pliny less accur^
ate
eight-year cycle. Tidal tables were frequently attached to
computi written after Bede's time.
Compared with the science of the twentieth century, and
even with that of the thirteenth century, Bede's was humble
enough, but against the ofits background time it was a remark'
able achievement. It contributed substantially to the Carolina
gian renaissance on the Continent, and found its way into the
educational tradition dating from the cathedral schools estab'
lished for Charlemagne by Alcuin ofYork. Bede's treatises on
the calendar remained standard textbooks for five centuries,
and were used even after the Gregorian reform of 1582; De
Temporum Ratione is still one of the clearest expositions of the
principles of the Christian calendar.
Besides Northumbria, Anglo-Saxon England saw some
scientific developments in Wessex. In the seventh century
astronomy and medicine were taught in Kent, there is evidence
that surgery was practised, and Aldhelm, abbot of Malmev
bury, wrote metrical riddles about animals and plants; but
the most notable contribution came in the first half of the
tenth century in the Leech Book of Bald, who was evidently a
physician living during or shortly after the reign ofKing Alfred,
to whom the book contains allusions. The Leech Rook gives a
5526.2 O