340 Mr. H. Bell on Atomit Number and 



in i^for Li, Na, K, Rb, Cs, although the Cs value is slightly 

 too great. Furthermore, two other elements in the column, 

 Cu and Ag, fall on a branch line passing through K. There 

 is thus a two-fold collinearity in the same vertical column of 

 the table, one line branching off from the other just where the 

 column itself seems to divide. A similar feature will be met 

 with again in the next column. Au forms an apparent 

 exception. It is sometimes regarded as having doublets 

 (although no series is claimed) with \Jv— V3817 as shown 

 by the cross, whereas the straight line indicates */v= V3167. 

 This point will be discussed later. 



In the alkaline earth column there are both doublets and 

 triplets (i/ 1? v 2 ) and the resulting collinearities are shown in 

 fig. 2. As regards the v-line a lower value for Mg would 

 fit in better with Ca, Sr, and Ba. It is noticeable, from the 

 table below, that such a modified value falls well in line with 

 the " branch" elements Zn and Cd. For the triplet series 

 there is a pair of straight lines for each of v l and v 2 , due to 

 branching at Mg, as the table itself suggests. In the case 

 of v 2 Ba has too low a value, 370 cm. -1 instead of 401 cm. -1 , 

 and Mg is again anomalous. A dotted line has been drawn 

 for v x as being more hypothetical ; it appears to branch off 

 for Zn and Cd to the right of Mg, and the usually accepted 

 series for Hg give differences that lie too high *f. 



For the next column Al, Ga, In are collinear (fig. 1), but 

 doubt has been expressed J that the doublet intervals for Ga 

 are known. The same remark applies still more strongly to 

 Be. sjv for Tl is certainly not collinear with Al and In, 

 being 7792 cm. -1 instead of 6323 cm" 1 . We might plead 

 in extenuation that the rare earths intervene in this column, 

 but the explanation given below seems more probable. Series 

 for< Scandium § and Yttrium are not known. 



Differences in the Carbon column are so little known that 

 it is not possible to discuss it in this manner. 



In the Nitrogen column no series have been found, but in 

 As, Sb, and Bi Kayser and Bunge || discovered a new type 



* It is noteworthy that the interval 1545'45 cm.- 1 , stated by Dunz, 

 loc. cit., as being preferred by Paschen, agrees fairly well with the value 

 1598 cm. required by the Zn, Cd line. 



t The branching phenomena in these two columns is analogous to a 

 result obtained by Rudorf, loc. cit. Plotting v/A 2 against A, where A is 

 atomic weight, he obtained curves for these families intersecting at these 

 elements. There is no numerical test applied. 



I Kayser, Spektroscopie, ii. p. 547. 



§ The series in Sc suggested by Hicks, Phil. Trans. A. ccxiii. p. 408, 

 give an interval of 320 cm.- 1 ; the line would give 350 cm.- 1 . 



|| Abh. Akad. Wiss. Berlin, 1893. 



