246 I)E. W. GEOFFREY DUFFIELD ON THE 



intensity is calculated, these are shown by the circles. Since the high-valued lines 

 10, 247, 213, 217, and 87 possibly form a separate sub-group, more cogent evidence 

 is perhaps afforded by the absence of low values for the displacement of lines of great 

 intensity. 



It remains to be proved whether the phenomenon is subjective or objective, whether 

 it may be explained by a tendency for the computer to read high values when the 

 density of the silver deposit is great, or whether the amount of energy involved in a 

 line does actually influence the displacement. One reason which may be urged for 

 regarding the phenomenon as independent of the observer is that intense lines are 

 usually broad and consequently more closely resemble lines under higher pressure ; 

 these have, however, been shown to be relatively less displaced than lines at lower 

 pressure, hence there would not seem to be any satisfactory reason for regarding the 

 measurements of the displacements of intense lines as being too large. If the energy 

 is responsible for the magnitude of the displacement one further enquires whether the 

 increased intensity is due to a larger number of vibrating particles, or to their 

 possessing greater amplitudes or to a combination of the two ; thus if the phenomenon 

 is objective it involves the dependence of the displacement either upon (l) the density 

 of the particular atom or modification of the atom responsible for each line, or (2) 

 upon the amplitude of its vibration. In any case the dependence of the displacement 

 upon the energy involved in a line is not the only factor concerned, since some faint 

 lines have very large displacements. 



The former would seem the more probable, but attempts to show that the 

 displacement of the line of an element is due to partial pressure have hitherto not 

 been successful. This will be discussed elsewhere ; the present discussion suggests 

 that the partial pressure effect due to the density of similar atoms is superposed upon 

 an effect due to the total pressure. 



10. Foreign Metals in the Spectrum of Nickel,. In addition to the nickel lines 

 whose displacements have been measured, a large number of lines due to impurities 

 appear in the spectrum, especially between \ = 3800 and X = 4100. They have been 

 measured, and their displacements will be found in the following table. As they have 

 been examined at several pressures, it should be possible to ascertain whether the 

 " density " of the element has any effect upon the displacement by comparing the 

 displacements of the lines produced respectively by pure poles and by small traces of 

 the element. 



