146 MORRIS LOEB 



elements of the intervening even-numbered series, and vice 

 versa, so that it has been found expedient to make two divi- 

 sions of each group, as will be seen in the table, the odd- 

 numbered series being set upon one side, the even-numbered 

 upon the other. In the eighth group occur triplets of closely 

 analogous elements to be discussed below. Arrangements into 

 fifteen or more individual groups, in place of the twin and 

 triple groups here shown, have been suggested, but not gen- 

 erally adopted. Mention should also be made of the fact that 

 this table can be constructed by writing the elements in the 

 order of their atomic weights along a screw-line of slight pitch 

 upon the surface of a cylinder, and then, as it were, unrolling 

 the cylinder. Various efforts have been made to connect all 

 the atomic weights by a graphic equation, which would pro- 

 vide for an arrangement on some other kind of a spiral curve, 

 either on a plane or in space, but they have been only moder- 

 ately successful. 



Before proceeding with a discussion of the details of the 

 table, it may be well to inquire what significance can be at- 

 tached to this periodic variability of properties as functions 

 of the atomic weight. The many attempts to connect the 

 atomic masses themselves in arithmetical relations would 

 indicate a widespread opinion that the substances now called 

 elements are really compounds of simpler substances, whose 

 particles have a finite mass and represent individuals of dis- 

 tinct chemical properties, so that the chemical elements in 

 each of the periodic groups might be likened to one of the 

 "homologous series" of organic compounds. This view really 

 antedates the periodic law, but fails in large measure to ac- 

 count for the resemblance existing between adjacent members 

 of different groups. Many, especially Sir William Crookes, 

 have held that the atoms are really fortuitous agglomerates 

 of an indifferent primordial element, and that atoms of ap- 



