39 JOURNAL OF THE 



used by de Chancourtois in his really remarkable work 

 has been the favorite method of illustrating- it. It has 

 been followed by Lothar Meyer, Mendeleeff, Gibbes, 

 Baumhauer, von Huth, Carnelley and others. Probably 

 a better method for class and teaching- purposes is the 

 pendulum-like diag-ram of Spring-, used also by Reynolds 

 and Crookes. Mendeleeff's objection to the curves of 

 Lothar Meyer seems to me valid thoug-h many prefer 

 to use these or similarly constructed curves. They 

 are, at any rate, scarcely suited to the needs of 

 the student who is indifferently equipped with math- 

 ematical ideas. Two objections can be raised to any and 

 all of these diag-ramatic illustrations. In the first place 

 they fail to bring- out some of the important conceptions 

 of the system, even obscuring- some of the points; and in 

 the second place, they g-enerally include fancies and spec- 

 ulations not essential to this system and not justified by 

 our present knowledg-e of it. They g-o too far and like 

 much teaching- of science by analog-y, are liable to be 

 presented by those using* them without due care and pre- 

 caution. This is especially the case wherever they are 

 looked upon as illustrating- the g-enesis of the elements, 

 about which we still know nothing- and should say 

 nothing-. 



Hartley puts the matter in this way. "The Periodic 

 Law can then be thus stated: The properties of the 

 atoms are a periodic function of their masses. In any 

 g-raphic representation of the periodic law the fact that 

 it is upon the mass of the atoms that their properties 

 depend should rppear prominently. The diagram of Dr. 

 Johnstone Stoney used to illustrate the "Log-arithmic 

 Law of Chemistry" has, on this account, alone a pre- 

 eminent importance." This diag-ram of Dr. Stoney 's could 

 scarcely be used by the average teacher because of its 

 complicated nature and the knowledge of mathematical" 

 operations required. Surely the greatest requirement is 

 clearness and simplicity. It should appeal readily to the 



