X.] 



THE " SERIES EVIDENCE. 



93- 



sented by the first constant of the first subordinate of the four groups,, 

 the theoretical wave-length limit lies 



Between 3498 '2 and 5065' 1 for lithium," sodium, potassium, rubidium, caesium. 

 3168 '6 3256 '0 copper, silver, gold. 

 ,, 2512*8 3222*6 magnesium, calcium, strontium. 

 2328*5 2490 '1 zinc, cadmium, mercury. 



In each group with the increasing atomic weight the spectrum 

 advances continually towards the red end ; also the distance between 

 the components of the doublets and triplets increases with the atomic 

 weights, so that for every group the distance is approximately propor- 

 tional to the square of the atomic weight. 



The Irregularities observed. 



The above account I trust will give a general idea of the new 

 investigation in its most general aspect. 



I have next to point out that we meet with most marvellous- 

 irregularities. We have some elements with many series, in others no 

 series have been detected, the numbers of the series varying even in 

 the gases. With regard to the metals, Kayser has suggested that the 

 melting point seems to have something to do with the phenomena 

 observed ; that is, that the higher the melting point the smaller 

 generally is the percentage of lines which is possible to distribute into- 

 series. The following table will show this : 



Relation of Series to Melting Points. 



The accompanying general table will show the facts touching these 

 various points which are at present known. The metallic elements. 



