IV.] THE SUN'S CHROMOSPHERE. 43 



The eclipse photographs, however, at the same time afford evidence 

 by the relative lengths of some of the lower temperature lines that we 

 need not locate the region which produces the absorption indicated 

 by the Fraunhofer lines at any great height above the chromosphere. 



I may say that for some time I was of opinion that in the sun many 

 of the darkest lines indicated absorptions high up in the atmosphere, 

 for the reason that the bright continuous spectrum of the lower levels 

 might have an important effect upon line absorption phenomena by 

 superposing radiation, and so diminishing the initial absorption. The 

 observations of the eclipses of 1893, 1896 and 1898, however, indicate 

 that this opinion is probably only strictly true when the strata of the 

 sun's atmosphere close above the photosphere are considered. 



Let us next turn to the highest regions of the solar surroundings to 

 see if we can get any effective help from them. 



In this matter we are dependent absolutely upon eclipses, and 

 certainly the phenomena observable when the so-called corona is 

 visible, full of awe and grandeur to all, are also full of precious teach- 

 ing to the .student of science. The corona varies like the spots and 

 prominences with the sun-spot period. 



It happened that I was the only person that saw both the eclipse of 

 1871 at the maximum of the sun-spot period and that of 1878 at mini- 

 mum ; the corona of 1871 was as distinct from the corona of 1878 as any- 

 thing could be. In 1871 we got nothing but bright lines indicating the 

 presence of gases, namely hydrogen and another since provisionally 

 called coronium. In 1878 we got no bright lines at all ; so I then 

 stated that probably the changes in the chemistry and appearance of 

 the corona would be found to be dependent upon the sun-spot period, 

 and recent work has borne out that suggestion. 



I have now specially to refer to the corona as observed and photo- 

 graphed in 1898 in India by means of the prismatic camera, remark- 

 ing that an important point in the use of the prismatic camera is that 

 it enables us to separate the spectrum of the corona from that of the 

 prominences. 



One of the chief results obtained is the determination of the posi- 

 tion of several lines of probably more than one new gas, which, so far, 

 have not been recognised as existing on the earth. 



Like the lowest hottest layer, for some reason or other, this upper 

 layer does not write ivs record among the lines which build up the 

 general spectrum. 



Up to the employment of the prismatic camera insufficient atten- 

 tion had been directed to the fact that in observations made by an ordi- 

 nary spectroscope no true measure of the height to which the vapours 



