566 The Evolution of Matter 



seemed quite unalterable, and the atoms, of which each element in 

 modern view is composed, bore to Clerk Maxwell, writing about 

 1870, " the stamp of manufactured articles " exactly similar in kind, 

 unchanging, eternal. 



Nevertheless throughout these years, on the whole so unfavourable 

 to its existence, there persisted the idea of a common origin of the 

 distinct kinds of matter known to chemists. Indeed, this idea of unity 

 in substance in nature seems to accord with some innate desire or 

 intimate structure of the human mind. As Mr Arthur Balfour well 

 puts it, " There is no a priori reason that I know of for expecting 

 that the material world should be a modification of a single medium, 

 rather than a composite structure built out of sixty or seventy 

 elementary substances, eternal and eternally different. Why then 

 should we feel content with the first hypothesis and not with the 

 second ? Yet so it is. Men of science have always been restive under 

 the multiplication of entities. They have eagerly watched for any sign 

 that the different chemical elements own a common origin, and are all 

 compounded out of some primordial substance. Nor, for my part, do I 

 think that such instincts should be ignored. . .that they exist is certain ; 

 that they modify the indifferent impartiality of pure empiricism can 

 hardly be denied 1 ." 



When Dalton's atomic theory had been in existence some half 

 century, it was noted that certain numerical relations held good 

 between the atomic weights of elements chemically similar to one 

 another. Thus the weight (88) of an atom of strontium compared 

 with that of hydrogen as unity, is about the mean of those of 

 calcium (40) and barium (137). Such relations, in this and other 

 chemical groups, were illustrated by Beguyer de Chancourtois in 

 1862 by the construction of a spiral diagram in which the atomic 

 weights are placed in order round a cylinder and elements chemically 

 similar are found to fall on vertical lines. 



Newlands seems to have been the first to see the significance of 

 such a diagram. In his "law of octaves," formulated in 1864, he 

 advanced the hypothesis that, if arranged in order of rising atomic 

 weight, the elements fell into groups, so that each eighth element was 

 chemically similar. Stated thus, the law was too definite ; no room 

 was left for newly-discovered elements, and some dissimilar elements 

 were perforce grouped together. 



But in 1869 Mendele"efF developed Newland's hypothesis in a form 

 that attracted at once general attention. Placing the elements in 



1 Report of the IWi Meeting of the British Association (Presidential Address, Cambridge 

 1904), p. 9, London, 1905. 



