302 M. F. Zollner on the Temperature and 



It must consequently be an admissible hypothesis that the tem- 

 perature and the quantity of hydrogen particles lying on the 

 visual line in a Geissler's tube agree with the analogous quanti- 

 ties at those places in the chromosphere the spectrum of which 

 corresponds with that of the Geissler's tube. 



It was shown above, in relating Wtillner's experiments, that in 

 general an increase of temperature operates in the same direction, 

 in relation to the widening of lines in the hydrogen-spectrum, 

 as an increase of density. So long, therefore, as the magnitude 

 of the effect of each of these two causes by itself is not more ex- 

 actly known, it would be conceivable that the same appearance 

 of the spectrum may take place with different values of the tem- 

 perature, if the corresponding values of the density and thickness 

 are present. But if one reflects on the considerable brightness 

 of the lines which in the chromosphere, in the immediate proxi- 

 mity of the brilliant margin of the sun, yet stand out distinctly 

 from the strongly illuminated ground of the spectrum, he will 

 be compelled to admit that the temperature of the glowing hy- 

 drogen in the chromosphere is at all events not below that at 

 which the hydrogen gas in a Geissler's tube exhibits the same 

 sharpness of the lines of the discontinuous spectrum. He will 

 hence be obliged also to suppose that the mass of the gas passed 

 through in the chromosphere by the visual line of the observer 

 is rather less than greater in comparison with that looked 

 through in the Geissler's tube. 



It is now easy, with the aid of the previously developed for- 

 mula (12), 



to derive a value for the density of the glowing hydrogen in a 

 defined stratum of the chromosphere. If we select the lower 

 boundary of it, in the above formula 



o", denotes the density (that is, the mass of hydrogen con- 

 tained in the unit of volume) in the lowest stratum of the 

 chromosphere, 

 m x the mass of hydrogen which, at the base of the chromo- 

 sphere, is passed through by our visual line, if the cross 

 section of the extent looked through is equal to the unit of 

 surface. 

 After the foregoing discussions this mass must, at equal tem- 

 perature, be supposed to correspond with that which, with equal 

 cross section, lies on the spark-track perpendicularly looked 

 through in a Geissler's tube. 



If the space occupied by the gas particles which are encoun- 



