42 INORGANIC EVOLUTION. [CHAP. 



prominences; and now, for the first time, a longer and thinner line 

 appears, occasionally noted as widened in spots ; while, last of all, 

 we get, very long, very delicate relatively, two lines constantly seen 

 widened in spots, and another line, not seen in the spark, and never 

 yet recorded as widened in spots.'* 



" This is one of the most mportant points in solar physics, but 

 there is not yet a concensus of opinion upon it. Professor Young 

 and others, apparently, still hold to the view first announced by Dr. 

 Frankland and myself in the infancy of the observations, that the 

 Fraunhofer absorption takes place in a thin stratum, lying close to the 

 photosphere." 



I next proceeded to discuss the numerous photographs obtained 

 during the eclipse, and I gave a map showing that there was only the 

 slightest relation between the intensities of the lines common to the 

 Fraunhofer and the eclipse spectrum, and further, that only a few of 

 the Fraunhofer lines are represented at all. Not only this, but in the 

 eclipse photographs there are many bright lines not represented at all 

 among the Fraunhofer lines. 



The chromosphere, which represents that part of the sun's atmo- 

 sphere underlying the true reversing layer, is admirably pourtrayed in 

 the photographs of the eclipse of 1898. So complete is the record 

 that it is quite sufficient for our present purpose, and is the more to be 

 relied on since it represents it at the same instant of time ; I have 

 elsewhere pointed out that Young's list of chromospheric lines may be 

 misleading because it is a summation of results obtained at different 

 times and of different conditions: prominences even may be, and 

 doubtless are, involved. The lengths and intensities of the lines are 

 faithfully recorded in the photographs. 



An examination of the eclipse photographs shows that the temperu : 

 ture of the most luminous vapours at the sun's limb is not far from 

 that produced by an electric spark of very high tension, the lines, 

 which we have seen to be enhanced on passing from the arc to such a 

 spark, being present. 



The chromosphere, then, is certainly not the origin of the Fraun- 

 hofer lines, either as regards intensity or number. From the eye 

 observations made since 1868, there is ample evidence that the quiescent 

 chromosphere spectrum indicates a higher temperature than that at 

 which much of the most valid absorption takes place ; in other words, 

 the majority of the lines associated with lower temperature are pro- 

 duced above the level of the chromosphere, and hence the true reversing 

 layer, instead of being at the bottom of the chromosphere, as held by 

 some, is really above it. 



* Proc. Soy. Soc., vol. xxxiv ; p. 297. 



