134 MJl. H. WILDE ON THE 



the spectrum, towards the more refrangible parts in the 

 inverse order of their atomic weights. The spectral lines 

 of .^=42 must therefore be sought for in the violet or 

 ultra violet part of the spectrum. The high refrangibility 

 of the lines which the missing element will have, may be 

 the reason why it has hitherto escaped detection, as from 

 the wide distribution in nature of its homologues of posi- 

 tion Ca, and K, in relation to their respective analogues 

 Sr and Rb, w = ^2 ought to be more abundant in nature 

 than gallium*. 



From the physical and chemical relations which subsist 

 among the halogens F, CI, Br, I, and the alkaline metals 

 Li, Na, K, Rb, Cs, chemists have already justly considered 

 these elements as positive and negative analogues of each 

 other and of hydrogen. In accordance with this view, I 

 have classified the halogens as negative forms of the series 

 Hw. By assigning to these elements the positions shown 

 in the table, it will be seen that besides the triad of atomic 

 weights formed by CI, Br, and I, there is a common 

 diiFence of 4 between the atomic weights of the halogens 

 and their positive homologues of position Na, K, Rb, and 

 Cs. Now if the groups of oxygen elements O, S, Se, Te, 

 be considered as negative forms of Uin, homologous in 

 character and position with the negative forms of }3.n, it 

 will be seen that besides the triad of atomic weights formed 

 by S, Se, and Te, there is a common difference of 8 between 

 them and their positive homologues Mg, Ca, Sr, and Ba ; 

 or double the common difference between the positive and 

 negative members of the series Jin. The oxygen elements 

 are multiples of 2, 4, 8, and 16, and may accordingly be 



* Nilson discovered in 1879 (Oomptes Eendus, Ixxxyiii. p. 645) a metal 

 with an atomic weight of 44, which he regards as trivalent, and has named 

 scandium. This metal, from several of its properties, would appear to be 

 x—/^z, H3W, and as all its homologues of position are well-known elements, 

 I have placed scandium (symbol Sc = 42) in the Table. — H. W. 1886. 



