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4. On the Red Prominences seen during Total Eclipses of 

 the Sun. Part I. By William Swan, F.R.S.E. 



The object of this communication is to discuss the evidence 

 afforded bj various observations of the eclipse which occurred on the 

 28th July 1851, as to the nature of the rose-coloured prominences 

 which are seen round the moon during the total phase of solar 

 eclipses. 



In order to render the inquiry into the nature of the red promi- 

 nences as complete as possible, the author has not confined himself 

 to the consideration of such hypotheses only as have been formally 

 stated regarding them ; but has also included in his examination 

 such other views as he thought might probably be entertained re- 

 garding those remarkable objects. 



The observations of the eclipse discussed by the author are chiefly 

 contained in the Royal Astronomical Society's Notice for January 

 1852, and the following are the conclusions to which he has been 

 led by the examination of those observations : — 



1. The red prominences were not caused by the telescopes used 

 in viewing the eclipse ; for they were seen by the naked eye. 



2. The red prominences cannot be regarded as optical phenomena, 

 produced either by unequally heated air, as supposed by M. Faye, 

 or by the action of the moon's limb on the sun's light ; for these 

 hypotheses are inconsistent both with the permanency of form dis- 

 played by the prominences, and with the general similarity of their 

 appearance, as seen from stations differently situated with reference 

 to the line of central eclipse. 



3. While the optical hypotheses thus labour under difficulties 

 peculiar to themselves, the objections to the opinion that the red 

 prominences are material objects existing in the sun, founded on the 

 discrepancies in the observations, as to their number, forms, and 

 positions, are found to apply with equal force to the optical hypo- 

 theses. 



4. Little care seems, in some instances, to have been taken in 

 ascertaining the positions of the red prominences, and accordingly 

 great discrepancies occur among the observations ; while in certain 

 cases they agreed remarkably well. Mr Dawes and the author, who 

 both used means for obtaining an accurate estimation of angles of 



