220 



DK. W. GEOFFEEY DUFFIELD ON THE 



has been .questioned, but in the writer's opinion they are real and not due merely 

 to unsymmetrical broadening ; it is true that the negatively displaced nickel lines 

 are more broadened towards the violet than the red, but the broadening takes place 

 about a negatively displaced position. Several theories can explain qualitatively 

 how displacements and unsymmetrical broadening towards the red may be accounted 

 for ; the displacement of a line towards the violet should not be more difficult to 

 explain than an unsymmetrical broadening in that direction ; the latter phenomenon 

 is unquestionably true. 



The following are the displacements of lines towards the violet measured by 

 Mr. PEARSE and by myself. The photographs were taken when the pressure of the 

 air was 10 atmospheres: 



TABLE V. 



Lint; 243 A = 508070 is apparently reversed and displaced towards the violet, but 

 this is found to be due to the strengthening under pressure of a faint line on its violet 

 edge. 



(5) Displacement Diagrams. In Diagram 1 lines are drawn connecting the 

 different readings of the displacements at different pressures of a few of the spectrum 

 lines dealt with, and each line represents the behaviour of one spectrum line. The 

 proportionality between the displacement and the pressure is apparent from the 

 diagram, and is approximately linear. In Section 7, p. 224, this point is further 

 examined. The diagram further illustrates the fact that the lines are capable of 

 resolution into two groups according to their rates of displacement, a feature which is 

 more fully treated later. 



The diagram includes both reversed and bright lines, but does not distinguish 

 between them. Without exception the former fall into the group with the 

 smaller displacement. Lines displaced towards the violet are not included in this 

 diagram. 



(6) Comparison with Previous Observations. The displacements of certain nickel 

 lines have been observed by HUMPHREYS and MOHLER* at pressures of 9f, 12^, and 



* HUMPHREYS and MOHLER, ' Astrophysical Journal,' vol. III., p. 114, 1896. 



