174 THE CHEMISTRY OF THE STARS. 



Let us next turn to the higher portions 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 I shall 

 fulfill my task very badly if I do not show you that the phenomena then 

 observable when the so-called corona is visible, full of awe and grandeur 

 to all, are also full of precious teaching to the student of science. This 

 also 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 

 anything could be. In 1871 we got nothing but bright lines, indicating 

 the presence of gases; namely, hydrogen and another, since provision- 

 ally called coronium. In 1878 we got no bright lines at all, so I 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 this year 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 position 

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

 not been recognized as existing on the earth. 



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

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

 general spectrum. 



GENERAL RESULTS REGARDING THE LOCUS OF ABSORPTION IN 

 STELLAR ATMOSPHERES. 



We learn from the sun, then, that the absorption which defines the 

 spectrum of a star is the absorption of a middle region, one shielded 

 both from the highest temperature of the lowest reaches of the atmos- 

 phere, where most tremendous chauges are continually going on and 

 the external region where the temperature must be low, and where the 

 metallic vapors must condense. 



If this is true for the sun it must be equally true for Arcturus, which 

 exactly resembles it. I go further than this, and say that in the pres- 

 ence of such definite results as those I have brought before you it is 

 not philosophical to assume that the absorption may take place at the 

 bottom of the atmosphere of one star or at the top of the atmosphere 

 of another. The onus probandi rests upon those who hold such views. 



So far I have only dealt in detail with the hotter stars, but I have 

 pointed out that we have two distinct kinds of coolest ones, the evidence 

 of their much lower temperature being the shortness of their spectra. 



