PERIODIC ARRANGEMENT OF ELEMENTS 163 



scarcely yet assumed the consistence of a theory, and 

 which are only at the present time to be ranked among 

 the poetic day-dreams of a philosopher'; and he pro- 

 ceeded : ' We seem here to have the dawning of a new - 

 light indicative of the mutual convertibility of certain 

 groups of elements, although under conditions which are 

 as yet hidden from our scrutiny.' 



Passing over attempts by Gladstone, Cooke, Odling, 

 and Strecker, we come to the years 1863 and 1864, when 

 John Newlands, in a series of letters to the Chemical 

 News, announced what he termed the ' Law of Octaves.' 

 His actual words were : ' If the elements are arranged in 

 the order of their equivalents, with a few slight trans- 

 positions, it will be observed that elements belonging to 

 the same group usually appear on the same horizontal 

 line. It will also be seen that the numbers of analogous 

 elements generally differ, either by 7 or by some multiple 

 of 7 ; in other words, members of the same group stand 

 to each other in the same relation as the extremities of 

 one or more octaves in music. Thus in the nitrogen 

 group, between nitrogen and phosphorus there are 7 

 elements; between phosphorus and arsenic, 14; between 

 arsenic and antimony, 14 ; and lastly, between antimony 

 and bismuth, 14 also. This peculiar relationship I propose 

 provisionally to term the " Law of Octaves." ' 



In 1869 and 1870, Lothar Meyer and Dmitri Mendeleeff, 

 independently of Newlands, and also of each other, 

 published papers in which they maintained that the 

 properties of the elements are periodic functions of their 

 atomic weights. This discovery goes by the name of the 

 'Periodic Law,' or better, the 'Periodic System.' The 

 arrangement of Meyer (p. 164), which differs but little 

 from that of Mendeleeff, is the one generally adopted. 



If this diagram is rolled round a cylinder, it will form a 

 continuous spiral, beginning with lithium and ending with 



