Physical Constitution of the Sun. 299 



while losing much of their sharpness; for an increase of the 

 density without a rising temperature can only, it seems to me, 

 effect the change into a continuous spectrum by widening the 

 lines, while by a rise of temperature, and therewith an increase 

 of the emissive power for all wave-lengths, the spectrum can just 

 as well become continuous in the other way." 



As is seen, these remarks do not touch, at all events, the ob- 

 servations of Wullner's I have quoted above, since the widening 

 of H a to a " band of several minutes breadth which has already 

 lost much of its sharpness," and " at the edges of which the 

 intensity of the light diminishes quickly," is expressly particu- 

 larized as a prominent feature. I believe, therefore, that at least 

 these observations can only be interpreted as they have been 

 in my theoretical investigation " On the Influence of Tempera- 

 ture and Density on the Spectra of Incandescent Gases," viz. 

 " that the spectra of gases in Geissler's tubes becoming conti- 

 nuous may be a consequence of an increase of the density of the 

 gas, as well as of its temperature being raised." 



The share of each of these two causes in the observed widening 

 of the lines and the continuity of the spectrum must of course 

 remain undecided until the dependence of the emissive and ab- 

 sorptive power on the temperature of the gas in question can be 

 ascertained. 



§ 6. 



If I now pass to a nearer discussion of the conditions under 

 which the knowledge of the necessary numerical quantities can 

 be attained, and at the same time make certain substitutions on 

 the ground of the hitherto roughly approximate values, I here 

 remark explicitly that I do so more for the purpose of illustrating 

 the theory developed than of deriving definitive values. This 

 remark is the more necessary as the temperature- values obtained 

 in a previous memoir, which I expressly designated as minima, 

 have been erroneously taken as definitive determinations. 



The observations above given in detail, on the modifications of 

 the hydrogen- spectrum with variation of the density and tempe- 

 rature, will in some measure put the reader in a position to form 

 an independent judgment on the question how far we have a 

 right to compare these variations to those which we observe in 

 the spectrum of the chromosphere. Considering that the diver- 

 sities of temperature at the lower and upper boundaries of the 

 chromosphere have a continual tendency to disappear through 

 the manifold and violent movements therein, while the move- 

 ments themselves owe their origin partly to those differences of 

 temperature, we may venture to ascribe the widening of the line 

 Hp, for example, at the base of the chromosphere in reality to 



