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IX. The Effect of Pressure upon Arc Spectra. No. 2. Copper, \ 4000 to X 4600. 



By W. GEOFFREY DUFFIELD, D.Sc., Honorary Research Fellow in Physics at 

 the University of Manchester, Mackinnon Student of the Royal Society. 



Communicated by Prof. E. KUTHERFORD, F.R.S. 



Received September 1, Read November 5, 1908. 



[PLATES 10-11.] 



CONTENTS. 



Page 



1. Preliminary 205 



2. Apparatus 206 



3. Behaviour of the copper arc under high pressures 206 



4. The photographs 207 



(1) Method of exposure 207 



(2) Description of the plates 207 



5. The broadening of the lines 208 



6. The displacement of the lines 209 



(1) Method of measurement of the photographs 209 



(2) Table I. of the displacement 209 



(3) Table II. of the displacement 211 



(4) Displacement curves 212 



(5) Eelation between the pressure, displacement and wave-length 212 



(6) Mean values of the displacement 215 



(7) Displacement and reversal of lines 216 



(8) Two-fold value of the displacement t 216 



7. Changes in relative intensity under pressure 218 



8. Series of lines in the copper spectrum 219 



9. 100 to 203 atmospheres [Added October 23, 1908] 222 



10. Summary of results 225 



1. PRELIMINARY. 



THE effect of pressure upon the arc spectrum of copper was first investigated by 

 HUMPHREYS and MOHLER,* who, in 1897, found that under pressures up to 

 14J atmospheres the lines became broader and were displaced towards the less 

 refrangible end of the spectrum. In 1907 photographs were obtained by 



* HUMPHREYS, ' Astrophysical Journal,' VI., p. 169 (1897). 

 VOL. CCIX. A 449. 14.12.08 



