260 Mr. M. M. Pattison Muir on Chemical Classification. 



stone, Cooke, Kremers, Pettenkofer, Odling, Newlands, and 

 others extended the observed points of connexion between 

 the atomic weights of the elements and their leading pro- 

 perties *. 



But it is especially to MendelejefFf fiiat we owe a syste- 

 matic attempt to correlate the leading properties, physical 

 and chemical, of the elements with the atomic weights of 

 these elements. 



Lothar Meyer i has also made important contributions to 

 the same subject ; and in his Modernen Theorien he has 

 gathered together most of the facts which have been as yet 

 established concerning the relations between atomic w^eights 

 and properties of elementary substances. 



31. The researches alluded to in the preceding paragraph 

 allow us to say that a very large degree of probability has 

 been established in favour of the hypothesis that the nature 

 of the chemical elements is a periodic function of their atomic 

 weights. 



" We may define a periodic phenomenon as one ^vhich, 

 with the constant and uniform change of the variable, returns 

 time after time to the same value" §. 



In the case before us we have as '' variable " " atomic weight;" 

 as " variant " we have the " nature of the chemical atom." In 

 the present state of our knowledge we cannot define this variant 

 with accuracy : hence it is not as yet possible, granting that 

 the ^^ nature of the chemical atom " is a periodic function of the 

 relative weight of that atom, to state quantitatively the nature 

 of this function. Nevertheless it may be possible to establish 

 roughly that the general nature of the atom does vary perio- 

 dically with the relati^-e weight of the atom. It is necessary 

 to break up the quantity ^^ nature of the chemical atom," and 

 to endeavour to show that such phenomena as specific volume, 

 malleability, ductility, electric position, power of forming 

 oxides, of forming chlorides, &c. &c. are really periodic 

 functions of the atomic weights of the elementary atoms. 



As I attempted to trace a connexion between physical pro- 

 perties of compounds on the one hand and chemical properties 

 on the other, and the composition or structure of these 

 compounds, so now would I endeavour to gather together a 

 few of the facts which show that the physical properties of 

 the elementary bodies vary periodically with the atomic 



• See Jahresherichte for 1851 to 1865. 



t Aoin. Chem. Pharm. Supj)^. Bd. viii. p. 133. 



X Ann. Chem. Phanji. SuppI.Bd. v. p. 129, and Suj^j^l. Bd. vii. p. 354, &c. 



§ Principles of Science; vol. ii. p. 61. 



