254 THE ATOMIC THEORY. 



longer seriously doubted. The curves of atomic volumes aud melting 

 points which Lothar Meyer afterwards constructed give strong sup- 

 port to this view. 



The periodic system, then, gives to the uum])ers discovered ])v Dalton 

 a much more profound significance than he ever imagined, and is 

 destined to connect a great mass of physical data in one general law. 

 That law we now see, "as in a glass, darkly;" its complete mathemat- 

 ical expression is yet to be found, ])ut I believe that it will ])e fully 

 developed within the near future. We may have a spiral curve to deal 

 with, as in the schemes proposed by Stoney or bj^ Crookes, or else a 

 vibratory expression like that suggested by Emerson Rey^nolds in his 

 presidential address before the Chemical Society last year; but in 

 some form the periodicity of the elements must be recognized, and 

 one set of relations will connect them all. 



In the arrangement proposed b}" Reynolds the inert gases, the 

 elements of zero valency, appear jit the nodes of a vibrating curve — a 

 circumstance which gives this method of presentation a peculiar force; 

 but for the consideration of physical properties the curves drawn by 

 Lothar Mey^er seem likely to be the most useful. In one respect, 

 however, the periodic system is still defective — it fails to take ade- 

 quately into account the numerical relations between the atomic 

 weights, a phase of the problem which should not be ignored. Such 

 relations exist; some of them have been indicated by your distinguished 

 fellow-member. Doctor Wilde; and, elusive as they^ may^ seem to be, 

 thev are surely not meaningless. The final law must cover the entire 

 ground, and then atomic weights, ph^-sical properties, and valency 

 will be completeh' correlated. Prout\s hypothesis is discredited, and 

 yet it may prove to be a crude ilrst approximation to some deeper 

 truth, as the probability calculations of Mallet" and of Strutf' would 

 seem to indicate. The approaches of the atomic weights to whole 

 numbers are too close and too frequent to be regarded as purely acci- 

 dental. But this is aside from our main question. The real point to 

 note is that the physical properties of the elements are all interde- 

 pendent, and that the fundamental constants are the atomic masses. 



Do I seem to exaggerate? Then look for a moment at the present 

 condition of pln^sical chemistry, and see how moderate my statements 

 really are. We have not only the laws already mentioned, of Avo- 

 gadro, of Dulong and Petit, of Faraday and of Mendeleetl', but also a 

 multitude of relations connecting the ph3\sical constants of bodies with 

 their chemical character. Even the wave lengths of the spectral lines 

 are related to the atomic weights of the several elements, as has been 

 shown by the researches of Runge and his colleagues, of Ruramel,'^^ 



«Phil. Trans., vol. 171, 1881, p. 1003. 



ftPhil. Mag. (6), 1, p. 311. 



cProc. Roy. Soc. Victoria, vol. 10, Part. I, \^. 75. 



