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598 MEDIEVAL ENGLAND
lettered craftsmen contributed in medieval England was chenv
istry. The learned were interested mainly in alchemy which, as
Roger Bacon described in his Opus Tertium, both included a
theory of matter and chemical change based on Aristotle's
conception ofelements and qualities, and as a practical subject
'teaches how to make the noble metals and colours ... not only
can it
yield wealth and very many other things for the
public
welfare, but it also teaches how to discover such things as are
human life . . /.
capable of prolonging
Bacon regarded science as a whole as a means of
obtaining
power over nature, power that would not only increase wealth
and health, but would also enable the
military forces of Chris>
tendom to overcome the Tarters and Antichrist, whose advent
he expected 'from beyond the Caspian gates'. Though no base
metal was ever transformed into gold, no elixir found to pnv
long life, no powerful weapon invented to repel at a blow any
possible invasion from the east, the pursuit ofthe objectives de^
scribed by Bacon did achieve some valuable results for chem^
istry and for science in general. Alchemists learnt to use the
balance, and discovered the properties of some metals, acids,
and other substances. Bacon himself referred, without giving
the recipe, to an explosive powder, and pointed out that its force
would be increased by enclosing it in an instrument of solid
material. Early in the fourteenth century Walter of Odington,
a versatile mathematician who made astronomical observations
at Oxford and wrote on optics and musical theory, composed
a most interesting treatise on alchemy in which he attacked con^
temporary alchemists, with their gold^making, as humbugs,
and tried to give mathematical precision to the whole subject.
He described various chemical processes, calcination, solution,
sublimation, congelation, and proposed a method of measuring
the qualities of dryness, heat, and so on in degrees represented
graphically by an adaptation of the procedures being worked
out by his contemporaries at Merton.
The most striking results in industrial chemistry pursued in
the middle ages in almost complete independence of learned
interests, were achieved in metallurgy, and this, even more than