EFFECT OF PRKSsrHE TPON ARC SPECTRA. GOLD. 

 (irnup TV. consists of the following lines : 



GROUP IV. 



71 



Further possibilities of finding groups of lines which are related to one another are 

 suggested by the tables of relative intensities and broadening. (See pp. 62 and 73.) 

 Of all the lines measured only one has been found to belong to any of the series 

 described by KAYSER and KUNGE. This is f2, \ = 506475, which, as far as we can 

 gauge from two measurements at different pressures, falls into Group 1 1 . 



The Zeeman effect has been investigated for only five of the above lines, so that 

 there are very meagre data for comparing the pressure and magnetic effects. The 

 magnetic separation, however, agrees in giving a smaller value for ll (Group II.) than 

 for c?2,/2, and r2 (Group III.). 



The values given by PURVIS* are as follows : 



(6) The Relation betiveen the Pressure and the Displacement. In the foregoing it 

 has been taken for granted that the relation between the pressure and the displace- 

 ment is a linear one, and there is no doubt that this is approximately the case, but it 

 is worth while examining the diagrams carefully to see if there is any indication of a 

 departure from this relationship and, if so, in what direction. 



In Diagram 1, which shows the amounts of the displacements at different pressures, 

 tlui values are higher at intermediate pressures than they should be if a straight line 

 is to describe the relationship correctly the lines are, indeed, slightly curved, being 

 concave towards the axis of zero displacement. 



Diagram 4 puts the matter more clearly ; in it each line represents the mean 

 displacement per atmosphere at different pressures, and the fact that the displace- 

 ments have been divided by a quantity which is constant for any one line need not 

 affect our discussion. Leaving out of consideration the values at 5, 10, and even 20 



* PURVIS, 'Proc. Canib. Phil. Soc.,' 14, 217, 1907. 



