[ 385 ] 



XLI. A Comparison of the Arc and Spark Spectra of Nickel 

 produced under Pressure; with a Note upon the Influence 

 of Temperature and ] J en sky Gradients upon the Displace- 

 ments of Spectrum Lines. By W. Geoffrey Duffield, 

 D.Sc, Professor of Physics and Dean of the Faculty of 

 Science in University College, Reading*. 



1. TI^HE appearance of Mr. Bilham's paper f upon the 

 X spark spectrum of nickel under 5 and 10 atmo- 

 spheres pressure suggests a comparison with the results of a 

 research upon the arc spectrum of the same metal $ when 

 subjected to pressure. 



In the following Table the successive columns give the 

 wave-length of the line with sufficient accuracy to enable it 

 to be identified, the intensity of the line in the spark and 

 arc spectra respectively, the displacements per atmosphere 

 calculated from the spark and arc readings at 10 atmospheres, 

 and from the arc readings at higher pressures (20 to 100 atmo- 

 spheres). The classification of the spark lines is given in 

 the two following columns, which are followed by descrip- 

 tions of the arc lines as regards broadening and reversal, and 

 their grouping in the arc according to their displacement 

 under pressure. The terms employed in the final columns 

 are explained at the base of the table. 



2. Comparing Bilham's readings at 10 atmospheres 

 (column A) with those of arc lines whose mean displace- 

 ments per atmosphere are calculated from both high 

 (column C) and low (column B) values of the pressure, 

 we have the following Table II., in which the spark lines 

 are divided up according to a classification suggested by 

 Gale and Adams and adopted by Bilham, in which 



Class I. includes lines which reverse symmetrically. 

 ,, II. „ „ „ „ unsymmetrically. 



„ III. „ „ „ remain brightandfairlynarrow. 



„ IV. „ „ „ „ „ but are much 



broadened symmetrically. 



,, V. ,, „ „ become very much broadened 



unsymmetrically towards the red. 



To facilitate comparison with the arc lines I have denoted 

 these in Table I. by r s , r v , s, gb B , g b r respectively. 



* Communicated bv the Author. 



t Bilham, Phil. Trims. Roy. Soc. A. ccxiv. p. 3o9 (1914). 



X Duffield, Phil. Trans. Roy. Soc. A. ccxv. p. 205 (1910;. 



Phil. Mag. S. 6. Vol. 30. No. 177. Sept. 1915. 2 C 



