99 PRESIDENT’S ADDRESS—SECTION A. 
atom (¢), and Lucretius appears to have thought that three was 
the smallest number of parts, angles, or sides [ 7] that an atom 
could have. Some were extremely small as compared with 
others, some smooth and round, others larger and more hooked 
and intertangled ; infinite the number of each shape. Differ- 
ences of density were attributed to the greater volume in the 
voids in bodies, differences of cohesion to the mode of union of 
the atoms. Violence and catalytic agents of all kinds would be 
ineffective but for the existence of the voids; they operate not 
on the atom itself, not, that is, on the perfectly hard and invul- 
nerable first beginnings of bodies; they merely separate atom 
from atom. Such views are essentially similar with those cur- 
rent to-day; is not, for example, Lucretius’ theory of limited 
variety really the beginning of the modern doctrine of elements ? 
Even those who imagine that the mother-stuff, so to speak, of 
the atoms, the prima materia, or protyle, is one, yet believe 
that the atoms themselves have intrinsic ard inviolable differ- 
ences of shape or density, and probably no physicist of to-day 
hesitates to ascribe differences in the chemical elements to con- 
stitutive differences in their atoms. 
9. Some Peculiarities of Lucretius’ Atoms.—Mention has 
already been made of Lucretius’ “hooked” atom. The notion 
has been criticised as crude. Thus Newton :—‘The parts of 
all homogeneous hard bodies which fully touch one another stick 
together very strongly, and for explaining how this may be, 
some have invented hooked atoms, which is begging the question.” 
| Why ?] But, after all, we have something not w holly dissimilar 
in modern chemistry in our conceptions of the mysterious link- 
age of atoms, and in our explanation of the strange activity of 
the status nascendi, even though we do not regard the lnks as 
material bodies. 
Two other remarkable features of Lucretius’ doctrine are his 
assumption of incessant motion under all circumstances, and his 
declaration that atoms in forming bodies must unite 7m conczlvo. 
In regard to the former he says :—‘‘ In some bodies the atoms 
rebound, leaviag smaller intervals, in others larger. In a mass 
of iron or stone the atoms are entangled, and can only throb or 
oscillate, moving to and fro very small distances; in softer 
bodies the atoms rebound at greater intervals” (v). 
Democritus had taught that like atoms are mutually attracted, 
and that the whirling motion to which they were subject sifted 
them with respect to size and form. The idea of Lucretius was 
more significant. Atoms, he held, must combine in a specific way 
[c.e., 2m concilio] to produce bodies. May we not, as Masson 
eke (v), fairly regard this as a foreshadowing of the molecular 
(t) wepi Ths &v TH aTOpmy yovias. 
(u) II. 97—108. See Masson Op. cit., p 38. (v) Op. cit., 
