118 Mr. H. M. Vernon on the 



The reason of this is that the extra elements in the eighth 

 group are only found attached to the even series 4 and 6 ; 

 if only one series were introduced between those commencing 

 with caesium and gold, then the extra elements osmium, 

 iridium, and platinum in the eighth group would come in an 

 uneven series. Also, if only one series were introduced, 

 the difference between the atomic weights of caesium and 

 gold would be 63' 3, which is not nearly so similar to the 

 difference between the atomic weights of caesium and rubi- 

 dium, which is 47*7, as that between caesium and copper, 

 which is 69*7. Also still further reasons will be shown to 

 exist why this extra series should be introduced. 



Of the elements in the list, lanthanum, cerium, and didy- 

 mium without doubt take their places in the eighth series in 

 the third, fourth, and fifth groups respectively. The next 

 two elements in order of atomic weight are samarium (150) 

 and mosandrium (153*6) : Where must these two elements be 

 placed ? Their atomic weights compel them to be placed in 

 this series, and they evidently cannot be placed in the sixth 

 and seventh groups. They must therefore find their place in 

 the eighth or extra group. There seems to be no reason why 

 they should not ; for the elements iron, nickel, and cobalt 

 form compounds of the form E 2 3 , and indeed the stablest 

 compounds of iron are grouped under this formula. Also 

 the elements composing these minor groups in the eighth 

 group resemble each other very greatly in almost all their 

 properties ; in the same way does samarium resemble mos- 

 andrium in its properties ; and when another element of the 

 atomic weight 151 is discovered to fill up the gap between 

 these two elements, as will very probably be the case, there 

 is every reason to expect that it w T ill show very great 

 analogies to the other two elements in the same minor group 

 as itself. If these elements, samarium and mosandrium, had 

 not been discovered, their existence might readily have been 

 predicted, as a minor group of elements in this eighth group 

 belonging to the eighth series is so evidently needed to bring 

 this series into harmony with the fourth, sixth, and tenth. 

 We see in this also additional evidence for the introduction 

 of two series between these commencing with caesium and 

 gold. 



The next element on the list is holmium, the place for 

 which in the table is evidently the third group in the ninth 

 series. 



Next comes the element terbium, the atomic weight of 

 which was found to be 124*7 on the supposition of its oxide 

 having the formula Tb 2 3 . We see that there is no place for 



