226 ON THE EFFECT OF PRESSURE UPON ARC SPECTRA. 



6. The lines belonging to the first and second subordinate series have greater 



displacements than the non-series lines. Their great width precludes accurate 

 measurement. 



7. The displacements of non-series lines are functions of their wave-lengths. The 



evidence indicates that they vary with a power of the latter at least as great 

 as the third and possibly as great as the sixth. 



8. There is some reason to believe that there are two values for the displacement ot 



a line at one and the same pressure. 



9. The mean displacement of the non-series lines is 12'2 thousandths of an 



Angstrom unit per atmosphere. The largest displacement measured is a little 

 more than 2 A.U. at 203 atmospheres.* 



777. Reversals: 



None of the copper lines within this region showed any signs of reversal under 

 pressure. 



IV. Relative Intensities: 



Within the region X 4000 to X 4600 : 



1. Changes in relative intensities of lines occur under pressure. 



2. Those belonging to either the first or second subordinate series vanish at about 



70 atmospheres and do not reappear as the pressure is increased. 



3. Members of the first sub-series become at low pressures faint and hazy, almost 



resembling bands, and are, at high pressures, dissipated. There is, however, 

 always a marked cloudiness in the neighbourhood of their original positions. 



4. Members of the second sub-series gradually diminish in intensity without 



abnormal widening. No cloudiness is distinguishable near their original 

 positions. 



5. Of the non-series lines those that are nebulous are strengthened relatively to 



those that are sharp. 



6. Lines strengthened under pressure do not correspond with those given by other 



workers as " enhanced " lines. 



V. Brightness: 



The brightness of the copper arc increases enormously with the pressure of the 

 surrounding air. 



I take this opportunity of thanking Dr. SCHUSTER for his advice and continued 

 interest in this work, which was undertaken at his suggestion, and I also thank 

 Prof. EUTHERFORD for having placed the necessary apparatus at my disposal. 

 Mr. R. Rossi, B.Sc., and Mr. W. C. LANTSBERRY rendered valuable assistance in the 

 high-pressure work, which I have pleasure in acknowledging. 



* Added October 19, 1908. 



