30 REPORT 1871. 



On Democritus and Lucretius, a Question of Priority in the Kinetical Theory 

 of Matter. ByT. M. Lindsay and W. R. Smith. 



Physicists who have recently called attention to the anticipation of modern 

 doctrines as to the ultimate natiu-e of matter by the ancient atomists, have looked 

 too exclusively to Epicurus and his expositor Lucretius, to the neglect of Demo- 

 critus and Leu3ippus. Democritus had no such expositor as Lucretius, but his 

 main views are accessible in the fragments collected by Mullach, and in the well- 

 known references of Aristotle, Simplicius, and Laertius. With the help of these 

 sources, the paper sketches the main features of the earliest atomic theories. The 

 following are leading points : — 



Democritus and Leucippus trace the variety of phenomena to three primitive 

 diflurences in tlie ultimate elements of nature, viz. differences (1) in Figure, o-;;^^/xa, 

 as between A and N ; ( 2 ) in Order, tci^is, as AN , NA ; (3) iu Position, ^eVty, as 

 Z, N [Arist. Met. A. 4]. From the motion in vacuo of atoms with these primary 

 differences, the whole variety of nature is deduced, generation and corruption being 

 merely syncretiou and division (a-vyKfua-is, Sidxpio-tj) [Ar. De Gen. et Cor. i. 8, 

 i. 2, Phys. viii. 9]. All atoms have the same density and the same opfifj ttjs (j>opas 

 (specific gravity ?) [Ar. Dj Ccelo, i. 7, Theophrastus De Sensu, 71]. Hence all 

 tend to fall in one downward direction * ; but being ignorant of the law of inertia, 

 Democritus supposes that the larger atoms fall faster, impinge on lighter particles, 

 and produce a vortex motion (SiVr;). In this vortex similars come together and 

 cohere, lighter particles go to the surface, and at length worlds (Kotr/not) are gene- 

 rated [Diog. Laertius, ix. 31J. Epicurus differs from Democritus mainly by main- 

 taining that all atoms have equal and invariable downward velocities, and come 

 into collision only by fortuitous automatic deflection from the line of fall. The first 

 half of this theory /oaks like the first law of motion, but is really as far from being 

 in harmony with the laws of acceleration and other known truths as the earlier view. 

 As physicists, therefore, Epicurus and Lucretius made no advance on Democritus, 

 while by mixing up with legitimate physical speculation the incongruent mdcqihynical 

 notion of chance (not the mathematical notion of chance, which plays a part in the 

 modern kinetic theory of gases), they produced that hybrid of physics and meta- 

 physics, a materialistic philosophy. It was by adopting the Epicurean doctrine 

 of chance that Gassendi, the first of modern atomists, became also the father of 

 modern materialism. 



Speculations on the Continuity of the Fluid State of Matter, and on Relations 

 between the Gaseous, the Liquid, and the Solid States. By Prof. James 

 Thomson, LL.D. 



Through the recent discovery of Dr. Andrews on the relations between dif- 

 ferent states of fluid matter, a difiiculty in the application of om- old ordinary 

 language has arisen. He has shown the existence of continuity between what is 

 ordinarily called the liquid state and what is ordinarily called" the gaseous state 

 of matter. _He has shown that the ordinary gaseous and ordinary liquid states 

 are only widely separated forms of the same condition of matter, and may be 

 made to pass into one another by a course of continuous physical changes pre- 

 senting nowhere any interruption or breach of continuity. If, now, there be 

 no distinction between the liquid and gaseous states, is there any meaning stiU 

 to be attributed to those two old names, or ought they to he abandoned, and 

 the single name the fluid state to be substituted for them both ? The answer 

 must be that in speaking of the whole continuous state we have now to call 

 it simply the fluid state; but that there ai-e two regions or parts of it, meet- 

 ing one another sharply in one way, and merging gradually into one another in a 

 difterent way, to which the names liqtiid and (/as are still to be applied. We can 

 have a substance existing in two fluid states diflerent in density and other proper- 

 ties, while the temperature and pressure are the same in both : and we may then 

 find that an introduction or abstraction of heat without change of temperature or 

 of pressure will effect the change from the one state to the other, and that the 



* Cf. the argument in Zeller, Phil, der Griechenj i. 913, ff. 



