ology. To him, it seems, we owe the idea of the three
'elements,' as they were and have been called, replacing the
old idea of the ancients of the four elements--earth, air,
fire, and water. It must be remembered, however, that both in
the ancient and the new idea the word 'element' was not
intended to mean that which it means to us now, a fundamental
unit of matter, but a general quality or property of matter.
The three elements of Valentine were: (1) sulphur, or that
which is combustible, which is changed or destroyed, or which
at all events disappears during burning or combustion; (2)
mercury, that which temporarily disappears during burning or
combustion, which is dissociated in the burning from the body
burnt, but which may be recovered, that is to say, that which
is volatile, and (3) salt, that which is fixed, the residue or
ash which remains after burning."

It is a little bit hard in our time for most people to understand just
how such a development of thoroughly scientific chemical notions, with
investigations for their practical application, should have come before
the end of the Middle Ages. This difficulty of understanding, however,
we are coming to realize in recent years, is entirely due to our
ignorance of the period. We have known little or nothing about the
science of the Middle Ages, because it was hidden away in rare old
books, in rather difficult Latin, not easy to get at, and still less
easy to understand always, and we have been prone to conclude that since
we knew nothing about it, there must have been nothing. Just inasmuch as
we have learned something definite about the medieval scholars, our
admiration has increased. Professor Clifford Allbutt, the Regius
Professor of Medicine at the University of Cambridge, in his Harveian
Oration, delivered before the Royal College of Physicians in 1900, on
"Science and Medieval Thought" (London, 1901), declared that "the
schoolmen, in digging for treasure, cultivated the field of knowledge
even for Galileo and Harvey, for Newton and Darwin." He might have added
that they had laid foundations in all our modern sciences, in chemistry
quite as well as in astronomy, physiology, and the medical sciences, in
mathematics and botany.

In chemistry the advances made during the thirteenth, fourteenth, and
fifteenth centuries were, perhaps, even more noteworthy than those in
any other department of