20 PRESIDENT’S ADDRESS—SECTION A. 
Troy (c). In view of the small extent of physical knowledge in 
the fifth and sixth centuries B.C., the age of Anaximander (d), 
and of his younger contemporary, Anaximenes (¢), of Miletus, of 
Heraclitus (f), Empedocles (g), and Plato (/), all of whom had 
opinions on the nature of matter, and that the evidence of the 
senses apparently strongly contradicts such a conception, its gene- 
sis must be regarded as remarkable. Metallic, crystalline, vitreous, 
gelatinous, albuminous, and liquid substances with which the 
ancients were familiar, are apparently continuous, and some of 
them might well have been regarded as structureless. And still 
more remarkable is it that the characteristic tendency of modern 
science, viz., the disposition to explain differences in phenomena 
by the assumption of mere variation of arrangement and move- 
ment in space, rather than by that of qualitative differences in 
matter per se, should at once have asserted itself. 
6. Anaxagoras, Leucippus, and Democritus.—Anaxagoras 
taught that objects were made up of constituent particles iden- 
tical therewith [homoiomeria], a doctrine at once challenged by 
Leucippus (7), and later by his pupil Democritus (7), both of 
whom regarded all atoms as qualitatively identical, and supposed 
differences in appearance and physical properties to be due 
partly to arrangement in space and partly to variety in form (A). 
The exact details of Leucippus’ doctrine have not been well 
ascertained ; indeed, Masson goes so far as to say that Leucippus 
is only a name to us (/). Nevertheless, from the references of 
Aristotle and others, it is evident that the fundamental concep- 
tions of atomistic physics, viz., that atoms and space are the ulti- 
mate constituents of all things, are due to him (m). Space he 
regarded as infinite, and, as already stated, atoms as qualita- 
tively, but not quantitatively identical. 
It has been supposed, on very insufficient grounds, that 
Democritus became an adept in the Egyptian mysteries, and that 
by Egyptian priests he was familiarised with the doctrine which 
he afterwards taught. There is no reason to doubt that it came 
from Leucippus. Despite this fact, and that to Leucippus, 
therefore, belongs the honour of having founded the atomic 
doctrine, it is with the name of Democritus that it is usually 
associated. This is not without some show of reason, for Demo- 
critus’ view was in all probability the more fully developed, and, 
moreover, he taught definitely what is tantamount to the so- 
(c) Chevreul. Histoire dela Matiére. Paris 4to, p. 349. 
(d) [611—547]. 
(e) [556 fi. ] 
(f) [535—475 2]. 
(q) [490—430 2]. 
(nh) [429—347]. 
(i Diog. Laert. De Vitis., lib. IX., ¢. 6. 
/) Mullach. Op. cit., I. 357—365. 
(k) Zeller. Philos. d. Griechen. I., pp. 704 ff., Aufl. 3. 
1) The Atomic Theory of Lucretius. p.3. 1884. 
(m) Pre-Socratic Philosophy. Vol. II., p. 296. Eng. Trans. 
