368 CLASSICS OF MODERN SCIENCE 

 that in observations made by an ordinary spectroscope no true measure 

 of the height to which the vapors or gases extended above the sun 

 could be obtained ; early observations, in fact, showed the existence of 

 glare between the observer and the dark moon ; hence it must exist 

 between us and the sun's surroundings. 



The prismatic camera gets rid of the effects of this glare, and its 

 results indicate that the effective absorbing layer — that, namely, which 

 gives rise to the Fraunhofer lines — is much more restricted in thick- 

 ness than was to be gathered from the early observations. 



We are justified in extending these general conclusions to all the 

 stars that shine in the heavens. 



So much, then, in brief, for solar teachings in relation to the record 

 of the absorption of the lower parts of stellar atmospheres. 



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 phenom- 

 ena 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 

 1 87 1 at the maximum of the sun-spot period and that of 1878 at 

 minimum; 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 

 provisionally called coronium. In 1878 we got no bright lines at all, 

 so I stated that probably the changes in the chemistry and appear- 

 ance 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. 



