EFFECT OF PRESSURE UPON ARC SPECTRA. NICKEL. 



227 



TABLE VII. 



-Katio of Displacement per Atmosphere at 10 Atmospheres Pressure to 

 Displacement per Atmosphere at Higher Pressures. 



doubt as to whether this is a subjective or an objective phenomenon. To the general 

 difficulties of measuring the displacement of spectrum lines reference has already been 

 made ; in particular it is not easy to compare the displacements of lines of different 

 width and whose intensity curves are of different shapes, but inasmuch as both 

 Mr. PEARSE and the writer agree in assigning values to the displacements at high 

 pressure which are smaller than they should be if a linear relationship exists, there 

 is good reason for regarding the pressure-displacement relation as not quite linear. 

 This is in accord with the results of the investigation of the gold spectrum under 



