764 THE POPULAR SCIENCE MONTHLY. 



shadow might not he entirely dark, and so to an observer might cause 

 the appearance of a bright fringe around the moon.* 



Not to speak of the recent evidence of the reality of the corona 

 from the photographs which have been taken when there is no inter- 

 vening moon to produce diffraction, there is the adverse evidence 

 afforded by the peculiar spectra of different parts of the corona, and 

 by the complicated and distinctly peculiar structure seen in the photo- 

 graphs taken at eclipses. The crucial test of this theory appears to 

 be that, if it be true, then the corona would be much wider on the 

 side where the sun's limb is least deeply covered, that is to say, the 

 corona would alter in width on the two sides during the progress of 

 the eclipse. Not to refer to former eclipses where photographs taken 

 at different times and even at different places have been found to 

 agree, the photographs taken during the eclipse at Caroline Island 

 show no such changes. M. Janssen says, " Les formes de la couronne 

 ont ete absolument fixes pendant toute la duree de la totalite." The 

 photographs taken by Messrs. Lawrence and Woods also go to show 

 that the corona suffered no such alterations in width or form as would 

 be required by Professor Hastings's theory during the passage of the 

 moon. 



We have, therefore, I venture to think, a right to believe in an 

 objective reality of some sort about the sun corresponding to the ap- 

 pearance which the corona presents to us. At the same time some 

 very small part of what we see must be due to a scattering of the 

 coronal light itself by our air, but the amount of this scattered light 

 over the corona must be less than what is seen over the dark moon. 



That the sun is surrounded by a true gaseous atmosphere of rela- 

 tively limited extent there can be little doubt, but many considera- 

 tions forbid us to think of an atmosphere which rises to a height 

 which can afford any explanation of the corona, which streams several 

 hundred thousand miles above the photosphere. For example, a gas 

 at that height, if hundreds or even thousands of times lighter than 

 hydrogen, would have more than metallic density near the sun's sur- 

 face a state of things which spectroscopic and other observations 

 show is not the case. The corona does not exhibit the rapid conden- 

 sation toward the sun's limb which such an atmosphere would present, 

 especially when we take into account the effect of perspective in in- 

 creasing the apparent brightness of the lower regions of the corona. 

 There is, too, the circumstance that comets have passed through the 

 upper part of the corona without being burned up or even sensibly 

 losing velocity. 



There can scarcely be doubt that matter is present about the sun 

 wherever the corona extends, and further that this matter is in the 

 form of a fog. But there are fogs and fogs. The air we breathe, 



* Report of the Eclipse Expedition to Caroline Island, May, 1883. Memoir of the 

 National Academy of Sciences, Washington. 



