31§ Prof, F. Zollner on the Temperature and 



§3. 



I now begin the discussion of numerical values with for- 

 mula (I,). The lowest value which can be assigned to t is 

 clearly 0. Hence we obtain for the internal temperature •t i the 

 minimum value 



,_•_ rHA ,~ 



* -* C (r + H) ' ^l 



Considering that the density of the solar atmosphere is re- 

 duced to an almost infinitely small quantity at a very moderate 

 distance from the sun's surface, and that the resistance thereby 

 offered is very slight, we may for the sake of simplicity make the 

 value of H equal to the mean height of the eruptive protube- 

 rances. A more exact discussion of the conditions under which 

 this may be done will be given hereafter. 



Protuberances are not unfrequently observed having an eleva,- 

 tion of 3 minutes ; but in order to be near the mark of a mean 

 value, I will take H to be 1*5 minute. 



The Heat-equivalent A I take to be equal to 5 J 5 expressed in 

 metrical and centesimal units. The product tec is taken to equal 

 3*409 for hydrogen, from the latest researches of Regnault*. 

 The value of k for hydrogen is, according to Dulong, l'411j\ 



A somewhat more detailed discussion is needed to obtain the 

 numerical value of r. According to the preceding, this signifies 

 the radius of the layer of separation through which the eruptions 

 break out. J The question is, does this value correspond with the 

 radius of the sun, or, in other words, is this radius identical with 

 that of the solar disk as we see it, or not ? 



The latest researches of Frankland and Lockyer, St. -Claire 

 Deville, and Wullner have shown that the discontinuous spec- 

 trum of hydrogen and other gases can be changed into a conti- 

 nuous bright one, the lines of the discontinuous spectrum under- 

 going a characteristic series of changes when the pressure is gra- 

 dually increased, which consist essentially in the widening of the 

 lines (as in the line H^), and in a corresponding diminution of 

 the distinctness of their boundaries. These changes render it 

 possible to come to some conclusion respecting the amount of 

 the pressure exerted at the given point; and Frankland and 

 Lockyer have already drawn conclusions on this subject, since 

 they say that IC at the lower surface of the chromosphere itself 

 the pressure is very far below the pressure of the earth's atmo- 

 sphere " J. ' 



* Pogg. Ann. vol. lxxxix. 



f Ann. de Chim. et de Phys. vol. xli. 



; Proc. Roy. Soc. vol, xvii. pp ? 288, 2 1. . . 



