26 The Past and Present of Chemistry. [Jan., 
the existence of which cannot be demonstrated, and which, when 
more closely examined, prove to be imaginary, was regarded as a 
mischievous fallacy. It was Robert Boyle, who, about the year 
1660, first expressed himself decidedly on this subject, and so 
laboured for the recognition of this truth, that we must regard it 
as having been established by him. From that time forth those sub- 
stances only were regarded as the constituents of bodies, which could 
be extracted from them by analysis, or which had been added to 
them by synthesis, and those substances only were considered to be 
elements which defied all known means of analysis. Further, these 
chemical elements were regarded as fundamentally different kinds of 
matter of the simplest constitution then known. 
What a contrast is exhibited between the ancient idea of the 
cause of difference in various forms of matter and that which ob- 
tained from the time of Boyle! If we consider these two opposite 
conceptions historically, and the transition from one to the other, 
they appear like two totally dissimilar pictures; but, like dissolving 
views, changing, the one into the other by slow degrees. In the 
first place we have the Aristotelian idea, according to which, matter 
itself devoid of properties, becomes endowed with characteristic 
qualities by the addition of properties, and forms, when invested 
with these properties, the various substances known in nature ; 
then this idea passes gradually into that of the alchemists, but 
becomes confused in the transition, inasmuch as the differences 
of physical conditions and properties are no longer regarded as the 
only causes of variety in substances; the difference in chemical 
properties receives more attention, the existence of elements, the 
producers of such properties is assumed ; and thus the path is pre- 
pared which leads to the idea of chemical composition. Then we 
see the Aristotelian theory gradually becoming indistinct, whilst 
the idea of the importance of the chemical deportment and compo- 
sition of bodies assumes prominence, and at last we see clearly that 
the differences between the substances which nature presents to us 
in such overpowering numbers, or which we have ourselves formed 
artificially, depend upon differences in their chemical composition. 
The idea of chemical composition, which makes its first appearance 
indistinctly in. the history of the chemistry of the middle ages, now 
forms the foundation of the science. In modern times a clear com- 
prehension of it is the essential condition of all progress. 
Turning to modern chemistry: we now recognize sixty-three 
different simple forms of matter which we term elements, and which, 
when combined, form all known compound substances. The dis- 
similarity of these elements and the difference in the modes and 
proportions according to which they are capable of combining, are 
now believed to be the causes of dissimilarity in those substances 
which are regarded as chemically different. Such dissimilar com- 
