300 M. F. Zollner on the Temperature and 



an augmentation of the density and thickness of the radiant 

 stratum of gas. Hence, in consideration of the proposition 

 above demonstrated (see p. 296), we can assume as the ratio 

 between the densities at the lower and upper boundaries of the 

 chromosphere the approximate ratio between the values of those 

 pressures within which, under terrestrial circumstances, the spec- 

 trum of hydrogen undergoes analogous changes in its constitution. 

 According to Wiillner's above-cited experiments, those values 

 would be, in round numbers, 2240 millims. and 1 millim. 

 Now, as the mean altitude of the chromosphere at the most 

 tranquil places on the surface of the sun may, according to the 

 observations, be taken at about 10 seconds of arc, we should be 

 in possession of those two numerical data which, with the help 

 of formula (3), furnish an approximate mean value for the abso- 

 lute temperature of the chromosphere. 

 The formula was 



t= gh } 



aul 

 in which 



I = log nat. — -- 



Taking as units the metre and the centesimal degree, we have 

 then 



<7=274-3, 



-=273, 

 a 



£ = 7153300, 



^ = 2240. 



if 



a = 1131600 (hydrogen), | 

 Herein 



p 



p ! is the specific gravity of mercury, 



g x the intensity of gravity at the surface of the earth, 



«j the mean barometric pressure, 



p the density of hydrogen under this pressure at 0° C. 



The resulting value of the absolute temperature is 

 t = 61350°. 



Here let me again give prominence to the circumstance that 

 the uncertainty of the numerical determination of the ratio — 

 affects the value of t only to a very small degree, because e. g. a 



