Secchi and Faye on the Sun. — Observations by Chacornac. 271 



objections to the theory of the solar photosphere and spots put 

 forth by Kirchhoff. 



He cites an opinion of Secchi, that as in our atmosphere 

 we have a substance — water — capable of transforming itself 

 into a fine dust* and into a vesicular state, capable of suspension 

 in clouds, so there may be in the solar atmosphere a quantity 

 of material capable of assuming* similar conditions at an elevated 

 temperature. 



These corpuscles would act like solid particles suspended in 

 gases, and would exert, as Magnus has shown, a greater 

 radiating power, both calorific and luminous, than the vapour 

 in which they floated. This would explain why the spots, or 

 places in which the clouds were torn and interrupted, radiated 

 less light and heat, although their temperature might? be the 

 same. 



If Kirchhoff was right in assuming that invisible layers of 

 an immense atmosphere external to the photosphere absorbed 

 certain solar rays, and thus produced the dark lines of the 

 spectrum, we ought to obtain from that outer atmosphere, when 

 its action could be isolated, a spectrum the exact converse of 

 that afforded by the photosphere. In 1842, M. Fasinieri took 

 advantage of a total eclipse to obtain this spectrum, and found 

 it completely dark in the space usually occupied by the green. 

 It was a discontinuous gaseous spectrum, and by no means the 

 converse of a solar spectrum. Bearing in mind these facts, M. 

 Faye thinks the absorption of certain rays may take place in 

 the photosphere itself, a supposition which would require us to 

 regard solar light as emanating not only from the surface of 

 the photosphere, but as also coming from various depths. If 

 the existence of a photosphere was preceded by a gaseous con- 

 dition in which no solid matter existed, researches, like those 

 of Mr. Huggins, may trace in other bodies the history of changes 

 which the sun has undergone. 



M. Faye observes that if the rice grains or willow leaves 

 owe their elongated form to currents in the sun's atmosphere 

 careful photographs made in the approaching period of the 

 minimum spots and least disturbance may show a noticeable 

 regularity in their direction. The disappearance of the rice 

 grains from, and the appearance of willow leaves and straws in 

 spots may, he thinks, be explained by supposing that in such 

 places there are strong descending currents, which cany the 

 bodies downwards and cause us to see them in elongated 

 perspective. 



He thinks the best photo-heliographs would be taken by 

 presenting the glass to the sun with the collodion surface behind 



* It is not correct to regard steam as water dust or fine spray. 



