Arc and Spark Spectra of Nickel under JPressiu 



1G0 



If Humphreys' data are included in obtaining the means 

 for the arc, the results are only slightly modified as in 

 Table III. 



Table III. 



Class. 



Number 



of 

 Lines. 



Mean Displacement per Atmosphere. 



Eatio 

 Spark : Arc. 



Arc (Humphreys 

 and Duffield). 



Spark. 



I. 



II. 

 III. 

 IV. 



V. 



11 



25 



6 



1 



8 



1-94 

 L64 

 l-f>5 



1-4 



8-84 



2-00 



184 



3-48 



7-7 



983 



103 

 112 



225 



5-50 

 Ml 



From an inspection of Tables II. and III. we arrive at the 

 interesting conclusion that the arc and spark shifts are, on 

 the whole, very nearly equal for lines in Classes I., II., and 

 V., but for lines in Class III. the spark displacement is 

 rather more than twice that in the arc. The values for 

 Class IV. rest upon the results for a single line, so that the 

 probability of error is too great to permit of any important 

 conclusions being drawn. It is a significant fact that 

 certain lines in Class V. show signs of reversal in the spark 

 under a pressure of eleven atmospheres. For example, the 

 reversal of the line I401"77, a typical specimen of this class, 

 can be distinctly seen in Plate i. of my original paper. In 

 the arc this line is given by Duffield as suffering immense 

 unsymmetrical broadening, without reversal even at the 

 highest pressures. If we regard the continuous spectrum, 

 which is so prominent in the more refrangible region of the 

 spark spectrum, as being due to immense broadenings of 

 lines of Classes I. and II. it is evident that Class V. 

 lines have something in common with those of Classes 1. 

 and II., although at first sight nothing could appear more 

 dissimilar. 



The view I have taken — namely, that Duffield's displace- 

 ments at ten atmospheres pressure are uniformly too high — 

 thus leads us to the conclusion that the behaviour of lines 

 easily reversed, or tending to reverse, is approximately the 

 same whether developed in the arc or spark under pressure. 



Phil. Mag. S. 6. Vol. 31. No. 182. Feb. 1916. N 



