[ 205 ] 





VIII. The Effect of Pressure upon Arc Spectra. 



No. 5. Nickel, \ 3450 to X 5500, including an Account of the Rate of Displacement 

 with Wave-length, of the Relation between the Pressure and the Displacement, 

 of the Influence of the Density of the Material and of the Intensity of the 

 Spectrum Lines upon the Displacement, and of the Resolution of the Nickel 

 Spectrum into Groups of Lines. 



By W. GEOFFREY DUFFIELD, D.Sc., Professor of Physics, and Dean of the Faculty 



of Science in University College, Reading. 



Communicated by Prof. A. SOHUSTER, Sec. R.S. 



[PLATES 1-5.] 

 Received May 28, Read June 25, 1914. 



CONTENTS. 



P?ge 



1. Preliminary 206 



2. Behaviour of the nickel arc under pressure 20G 



3. The photographs 200 



(1) Region investigated 206 



(2) Description of the plates 207 



4. The broadening of the lines 208 



(1) General features 208 



(2) Continuous spectrum 209 



5. The reversal of the lines 209 



6. Changes in the relative intensities of the lines 210 



7. The displacement of the lines 211 



(1) The measurement of the photographs 211 



(2) Table of displacement 213 



(3) The spectrum of the nickel arc under pressures of +155 and + 200 atmospheres . . 218 



(4) Displacements towards the violet. .. 219 



(5) Displacement diagrams 220 



(6) Comparison with previous observations 220 



(7) Relation between the pressure and the displacement 224 



(8) Relation between the displacement and the wave-length 228 



8. Resolution of the nickel spectrum into groups 236 



9. Relation between the intensity of a line and its displacement 244 



10. Foreign metals in the spectrum of nickel 246 



(1) The influence of the density of the material 250 



VOL. CCXV. A 530. 2 E [Published May 4, 1915. 





