LU [ROYAL SOCIETY OF CANADA 



The progress of modem science has tended to produce a strong 

 conviction of the truth of the theory. — The phenomena of diffusion in 

 liquids and gases, for example, tend to show that they not only consist 

 of particles, but that these particles are in constant motion. As aa 

 example in solids we have that remarkable experiment of Eoberts-Aus- 

 ten, in which a cylinder of lead was placed on top of a cylinder of 

 gold, and left for a considerable time in a warm chamber; when taken 

 and examined gold was found diffused throughout the lead, particles of 

 thJB the heavier metal having risen upwards as if they had wings. 



It is certain that the theory, which long preceded the dawoi of 

 experimental science, came to modem Europe from Ancient Greece and 

 it has been traced even to India. Strabo who lived in the reigns of 

 the Eoman emperors, Augustus and Tiberius, says that its author was 

 M'ochus or Moschus, of whom he speaks vaguely as more ancient than 

 the Trojan war. This would make the Greek- Theory not less than 

 three thousand years old and will mark it off from Dalton's Atomic 

 Theory which came into being only a century ago. 



We have more definite statements about Democritus as author of 

 the Atomic Theory and before him of Leucippus, although the writings 

 of neither survive. Lucretius, the contemporary of Cicero, expounded it 

 in his great poem " De Rerum Naturâ" — Thus it was transmitted to 

 modem times, and became familiar. ]!^ewton gives it a compact shape. 

 Dalton had firm faith in it. 



Dalton's Atomic Theory. 



From the emphasis with which Dr. George Wilson writes in his 

 account of Dalton's " Life and Discoveries," it would almost seem as if 

 he had foreseen the mistakes made about Dalton's Atomic Theory to-day. 

 He says, and re-iterates, that Dalton was an Atomist before he was a 

 Chemist — that he joined the Greek Atomic Theory, which he found m 

 lexistencei, with the Chemical Laws of combining proportions, but that 

 the laws rested on a perfectly independent basis of experiment- — ^that it 

 was unnecessary to concede to Dalton's atoms the attribute of indivisi- 

 bility, and that Dalton's contemporaries, Davy, Wollaston, Berzelius, 

 declined to employ the word atom, because it assumed indivisibility, and 

 that they substituted other words. In short, that the Greek Atomic 

 Theory and the Chemical Laws are independent one of the other. That 

 if the link forged by Dalton between the Greek Theory and the Experi- 

 mental Laws be broken, the Experimental Laws are absolutely secure, 

 while the Theory must stand or fall by its own merits. 



This expresses exactly the position to-day. The link has been 

 broken. The existence of bodies much smaller than those presented to 



