5
The Reality of Molecules
5a. About the Nineteenth Century, Briefly- Chemistry. In 1771 work was completed on the first edition of the Encyclo-
pedia Britannica, 'a Dictionary of Arts and Sciences compiled upon a new plan
... by a Society of Gentlemen in Scotland.' The entry atom, written by William
Smellie, a man renowned for his devotion to scholarship and whisky [Kl], reads
as follows. ''Atom. In philosophy, a particle of matter, so minute as to admit no
division. Atoms are the minima naturae [smallest bodies] and are conceived as the
first principles or component parts of all physical magnitude.' Democritus might
have disagreed, since his atoms were not necessarily minute. Epicurus might have
objected that the atom has structure—though it cannot be divided into smaller
parts by physical means. Both men might have found the definition incomplete
since it did not mention that atoms—as they believed—exist in an infinite variety
of sizes and shapes, any one variety being forever incapable of transforming itself
into any other. They might have wondered why no reference was made to the
irparrr] vXri, the prime matter of which all atoms are made. It is likely, however,
that an imaginary dialogue between the Greek and the late eighteenth century
philosophers might rapidly have led to a common understanding that in the two
thousand years which separated them very little had changed regarding the under-
standing of the basic structure of matter.
The period of rapid change began in 1808, when John Dalton commenced the
publication of his New System of Chemical Philosophy [Dl]. This event marks
the birth of modern chemistry, according to which all modes of matter are
reducible to a finite number of atomic species (eighteen elements were known at
that time). Dalton's early assessment (in 1810) of the youngest of the sciences
sounds very modern: 'I should apprehend there are a considerable number of what
may be properly called elementary principles, which can never be metamor-
phosed, one into another, by any power we can control. We ought, however, to
avail ourselves of every means to reduce the number of bodies or principles of this
appearance as much as possible; and after all we may not know what elements
are absolutely indecomposable, and what are refractory, because we do not know
the proper means for their reduction. We have already observed that all atoms of
the same kind, whether simple or compound, must necessarily be conceived to be
79