PRESIDENTIAL ADDRESS.—SECTION A. 
(Astronomy, Mathematics, and Pliysies). 
THE HISTORY OF THE ATOMISTIC CONCEPTION, 
AND ITS PHILOSOPHICAL IMPORT. 
By GEO. H. KNIBBS, F.R.A.S., UNIVERSITY OF SYDNEY. 
I. 
GENERAL HISTORY OF ATOMISM. 
1. Introduction.—Kach of the great branches of science, with 
which this section of our Association is concerned, covers so wide 
a range that it would be a hopeless task, in the brief time avail- 
able for an address, to attempt an adequate review of recent pro- 
gress therein. As an alternative, however, it may not be 
unprofitable to confine our attention to a subject, of interest 
alike to mathematician, physicist, and astronomer. I refer to 
our physical ideas of matter. To the mathematician, because 
the subject has afforded a dignified field for the exercise of his 
genius, and depends for its richest results upon the truths which 
he has secured through research—one may say—in the deepest 
recesses of Mind. To the physicist, because it covers the domain 
of Nature. To the astronomer, because in the wide reaches of 
Time and Space, opened up through his investigation, the 
material is identical with that with w hich we are all “familiar 
2. The Réle of the Atomic Conception.—The foundation of all 
physical theories regarding the constitution of matter is, of 
course, the atomic conception; and in that development of 
natural philosophy, which has formed so striking a feature of the 
century now closing, no other conception has played a more signi- 
ficant part. As the eroundwork of a general theory of matter, 
it has gone far to explain the gaseous, liquid, and solid states, and 
the whole range of phenomena connected therewith. To some 
extent it has made intelligible the morphology of crystals, and 
most optical facts in relation to crystalline structure; it has 
facilitated the apprehension of the facts of chemistry, and united 
them in a signal way ; and it may even be said that the majority 
ot the larger facts of physical science have, by its aid, been 
wholly or partially reduced to questions of mechanics. 
