292 M. F. Zollner on the Temperature and 



or, if h can be neglected in comparison with r, as a formula of 



approximation, 



<=fi ® 



§3. 



The spectroscopic examination of the margin of the sun per- 

 mits us to observe a portion of the incandescent hydrogen which 

 forms an essential constituent of the sun's atmosphere, in the 

 form of the so-called chromosphere,, and to determine the mean 

 altitude (h) of this stratum at those parts of the sun's margin 

 which by the absence of protuberances lead us to infer a certain 

 degree of equilibrium of the atmosphere. If, then, we were in 

 a position to ascertain even approximately the ratio of the pres- 

 sure or the density at the lower and upper boundaries of the 

 chromosphere, we should thereby attain possession of both those 

 empiric data which, by the employment of formula (2) or (3), 

 would afford us the calculation of a mean value of the tempera- 

 ture for the chromosphere. Since the required ratio does not 

 enter directly into the temperature-formulae, but only its natural 

 logarithm, the values of that ratio may vary within relatively 

 wide limits without thereby considerably affecting the tempera- 

 ture-value dependent thereon. If, for example, that ratio varied 

 between the values 500 and 5000, the natural logarithms of 

 these values would be relatively 6*2 and 8' 5 ; and therefore even 

 so great an uncertainty in the ascertaining of the pressure-ratio 

 would imply only a proportionally little alteration of the tempe- 

 rature-value which depends on it. 



We have now to inquire if there are phenomena which permit 

 us to infer an approximate value of the ratio of the pressure at 

 the base and at the ordinarily visible limit of the chromosphere. 



In my previous memoir on the temperature and physical con- 

 stitution of the sun, the investigations of Frankland, Lockyer, 

 Ste.-Claire Deville, and Wullner on the changes in the spectra 

 of gases with variations of the pressure formed the argument 

 which, I thought, justified me in assuming "that the pressure at 

 the base of the chromosphere, or at the extreme margin of the 

 luminous disk of the sun, must lie between those of 50 and 500 

 millims. of mercury at the surface of the earth" (/. c. p. 110). 



In a later memoir, however, " On the Influence of Density 

 and Temperature on the Spectra of Incandescent Gases"*, I 

 showed that, cateris paribus, the increase of density of a lumi- 

 nous gas must produce precisely the same effect as the increase of 

 the thickness of the luminous stratum — or, in other words, that 



* Berichte K. S. Ges. W. Oct. 31, 18/0. Phil. Mag. S. 4.vol.xli.p. 190. 



