﻿204 Influence of Density on the Spectra of Incandescent Gases, 



more or less deeply into the flame of a Bunsen's burner, enve- 

 lope different quantities of sodium vapour. With small quan- 

 tities the lines are fine and sharp ; with large quantities, much 

 widened, and the edges indistinct. 



But in this case the more refrangible of the two lines of sodium 

 ividens considerably more than the other, so that with the greatest 

 amount of vapour which can be developed in the given manner the 

 more refrangible line is fully twice as broad as the other. 



From this fact must be inferred, in accordance with § 8, 

 greater values of the absorptive power for the values of X be- 

 longing to the more refrangible sodium-line, and accordingly, 

 on account of the continuity of KirchhofFs function J, also 

 greater values of the emissive power. Both these consequences 

 are confirmed by observation. 



When the two sodium-lines in the solar spectrum are com- 

 pared, we find, on viewing them more carefully, the more re- 

 frangible decidedly darker than the other — a fact which proves 

 the greater absorptive power in this part of the spectrum. 



If, further, w T e compare the bright sodium -lines in any source 

 of light, we always find the more refrangible brighter than the 

 other, whether the vapour-density be great or small. This dif- 

 ference of brightness becomes even very striking when the fol- 

 lowing method of observation is employed. The slit of the 

 spectroscope is gradually opened till the inner edges of the lines 

 thus widened exactly touch. The adjacent bright bands then 

 show such a considerable difference in brightness, that it strikes 

 the eye at the first glance. By this observation, then, also the 

 greater emission for the values of \ belonging to the more re- 

 frangible line D is proved. 



In order, by observation of the sodium-lines, to verify the 

 asymmetry which, according to the theory we have developed, 

 was to be expected in the widening, with the aid of my reversion- 

 spectroscope I brought each of the bright sodium-lines in one 

 spectrum into coincidence with the analogous line in the other 

 spectrum, so that each line became the prolongation of the 

 other, and the two together apparently formed only a single line 

 of double the length. In the more refrangible line, which with 

 increase of the vapour- density was the most widened, no dis- 

 placement was perceptible; meanwhile there appeared to take 

 place in the other line, as the bightness increased, an extremely 

 slight displacement in the direction of a diminution of the refran- 

 gibility. 



Even if we attribute no force of proof to this observation, 

 as being too uncertain, yet, on the other hand, an interesting 

 observation made by Dr. J. J. Miiller, Private Instructor and 

 Assistant in Physics at the Physiological Institute in this place, 



