232 



DR. W. GEOFFEEY DUFFIELD ON THE 



adequate correction could be applied to the measurement of the lines in the neighbour- 

 hood of X = 4300 to 4400, which appear abnormally high in the diagram, and there is 

 little doubt that the readings are in fact rather too large. It has been stated that 

 for the sake of uniformity Mr. PEARSE'S readings have been used almost exclusively 

 in preparing the tables, my own readings of the lines serving as a check upon them. 

 The check readings in this region indicate that the measurements of the lines in 

 region 4800 to 4900 are to those in region 4400 as 5 is to 4. This would improve 

 Diagram 4, and also make the second group in Diagram 6, fig. 4, more compact by 

 reducing the displacements of lines 160, 167, 172, 174 and 176. 



The above argument is based upon the resolution of the nickel spectrum into only two 

 groups, but reasons will be given in the next section for distinguishing between three 

 groups. If this is the case we must consider whether the isolated lines between the 

 two main groups could form a group by themselves. If the displacement varies with 

 the square of the wave-length, Diagram 6, fig. 3, indicates that the following lines 

 would constitute it : 213, \ = 482918 ; 217, \ = 4855'57 ; and 247, \ = 5477'13. 

 The last-named is not of the same nature as the first two, and there is a considerable 

 separation between 213, 217, and the similar lines 87 and 165 which should be 

 associated with them according to their behaviour and general appearance. Five 

 more lines, 10, ID, 21, 2<i, 31, which resemble them by being nebulous at atmospheric 

 pressure, may also be associated with them. It will be seen from what follows that 

 they form a more compact group when classified according to the cube of the wave- 

 length. Though the determination is by no means conclusive, the balance of evidence 

 favours this rate of variation of the displacement. 



It is important to see to what extent the readings at 10 atmospheres confirm the 

 above conclusion. 



TABLE VIII. Displacements at 10 Atmospheres Pressure over Wave-length 



Squared and Cubed. 



