On the Corona of the Sun. 



119 



Captain Abney, F.R.S., who has the photographs taken, at Caroline 

 Island under examination, informs me that : — 



" The diffusion during that eclipse was not insensible,, as the lines 

 H and K are distinctly visible across the black moon as dark lines. 

 It is true that H and. K,. as bright lines, do stop at the moon's limb, 

 but these lines are not coronal lines, as they belong to the pro- 

 minences. In the Egyptian eclipse — which was a very short one — 

 the prominences were far over the moon's limb, and the diffusion 

 due to the atmosphere was such that the lines H and K were shown as 

 bright lines over the moon. In the Caroline Island eclipse the pro- 

 minences were much less marked and more hidden during the eclipse 

 than was the case in Egypt, and it appears that the diffusion by the 

 air must have been much greater in the former (Caroline Island) 

 than in the latter, since it is the light from the hidden sun which was 

 evidently reflected and re-reflected. On one side of the moon's limb 

 H and K are seen reversed, whilst on the other they are reversed 

 beyond the bright lines. 



" In both cases the reversals are rather faint, but as strong as the 

 reversal which was seen on the corona spectrum at the Egyptian 

 eclipse. In my opinion, in the photographs of the corona with the 

 longest exposure (I am not now speaking of spectrum photographs) 

 the moon is not shown as perfectly black, but I should not like to 

 found any theory very definite as to this, as it might be due to 

 over-development, but I think not." 



It should, be mentioned that during the time that Professor Hastings 

 observed the change in. length of the line 1474, photographs of the 

 corona were taken by M. Janssen, and by Messrs.. Lawrance and 

 Woods. M. Janssen says : " Les formes de la couronne ont ete abso- 

 lument fixes pendant toute la duree de la totalite."* The photographs 

 taken by Messrs. Lawrance and Woods show that the corona suffered 

 no such alterations in width and form as would be' required by Pro- 

 fessor Hastings' theory, during the passage of the moon across the sun. 



For other points raised by Professor Hastings, and for his discussion 

 ! of former spectrum observations of the corona, I must refer to his 

 memoir. f 



The evidence in favour of the corona being a true solar appendage 

 appears to me to be of overwhelming weight. It seems difficult on 

 any other hypothesis to explain satisfactorily — (1) the observed and 

 the photographed spectra of different parts of the corona ; (2) the 

 visibility of the planets Yenus and Mercury as dark bodies when near 

 the sun ; (3) the filamentous, and especially the peculiar curved 

 structures seen in photographs of the corona ; (4) the close agreement 

 of photographs taken at different times during an eclipse, and 



* " Annuaire pour l'An 1884," p. 859. 

 f Vide ante. 



