32 



THE NEW KNOWLEDGE. 



Concerning Sub-group A, we find in the table (Fig. 7) 

 the same progressive variation in steps. 



Fig. 7. 



Thus, if fluorine will do a certain thing, chlorine will do 

 it more, bromine still more, and iodine most. Or, it may 

 act the other way: If fluorine does a certain thing, chlorine 

 will do it less, bromine still less, and iodine least of all. The 

 important thing is that as the elements vary, they vary 

 progressively in steps as the atomic weight rises. The di- 

 rection of the arrows in the table shows the direction of the 

 progressive change for each property. Now what holds good 

 for Groups II and VII holds equally good for every other 

 group of the system. As a matter of fact, the elements of 

 matter fall naturally into a series of groups. Each group 

 falls naturally into two sub-groups, which have in certain 

 properties an unmistakable relation to each other, while the 

 constituent members of each sub-group resemble each other 



