THE SUN'S TRUE ATMOSPHERE. IOI 



of spectrum belonging to the region just outside the 

 sun's edge, which showed hundreds of bright lines. 

 Here seemed to be conclusive evidence of that shallow 

 atmosphere of glowing vapours in which Fr. Secchi 

 had faith. But Mr. Lockyer interpreted his observa- 

 tion differently. The presence of these vapours on 

 this particular occasion he regarded as wholly excep- 

 tional, and the cause of the exception he held to be 

 the energetic injection of vapours from beneath the 

 surface of the sun. 



At about this stage of the controversy I had occasion 

 to consider the problems associated with the physical 

 condition of the sun and his surroundings ; and although 

 I took no part in the discussion between Fr. Secchi and 

 Mr. Lockyer, I expressed (in papers which I wrote upon 

 the subject) opinions which agreed with the views of 

 the Italian astronomer. It is necessary for me to pre- 

 sent in this place my own reasoning on the question at 

 issue, because it not only serves to introduce the special 

 observation made last December, by which the problem 

 has been finally solved, but also presents certain con- 

 siderations which must be attended to in interpreting 

 that observation. 



In the first place, I noted that the darkening of the 

 sun's disc near the edge, or rather the marked nature 

 of that darkening, instead of showing (as had been so 

 often stated) that the sun has a very deep atmosphere, 

 proves, on the contrary, that his atmosphere must be 

 exceedingly shallow by comparison with the dimen- 

 sions of his globe. It is easy to show why this is ; and 



