Royal fnstifution. 513 



Perpignan, Superga, Lipetsk, the lowest of the red prominences was 

 not seen ; and that at Superga and Lipetsk only was the middle one 

 of the upper prominences seen, though in several places an irregular 

 band of red light had beeii seen of which one salient point might be 

 the prominence in question. In all the places where the order of 

 formation had been observed, the same prominence (the left-hand 

 upper prominence) was defined as the first seen. At Perpignan this 

 was observed by M. Mauvais to show itself first as a small point and 

 to project gradually as from behind the moon. The discordance in 

 these representations did not appear to the Lecturer at all startling ; 

 it was not greater than the discordance in the accounts given by two 

 good observers in difiFerent rooms of the same building at Padua. 



The determination of the locality and nature of these red promi- 

 nences is one of the most difficult of all connected with the eclipse. 

 The first impression undoubtedly was that they are parts of the sun. 

 If so, their height, at the lowest estimation, is about thirty thousand 

 miles. The principal objection, however, to their solar location is 

 the difference in their forms as seen at different places : thus at 

 Perpignan they are represented as widest at the top ; at all other 

 places they are widest at the base. Moreover at some places, as 

 Pavia and Vienna, where they were seen a long time, they under- 

 went no change ; whereas at Perpignan one at least was seen to 

 slide out as from behind the moon. In all cases, however, much is 

 to be allowed for the hurried nature of the observation. 



The only theory which has been formally propounded as explain- 

 ing them is that of M. Faye, who conceives them to be the result of 

 a kind of mirage. 



The Lecturer explained the nature of ordinaiy mirage (the kind of 

 reflexion produced by the hot air adhering to a heated surface of 

 any solid) and described the distortion produced in the image of a 

 star as seen in the Northumberland telescope of the Cambridge Ob- 

 servatory, when first mounted in a square pyramidal tube, whose 

 angles were constnicted move solidly than its sides, reducing the 

 inner form to an octagon. "When this tube had become warm before 

 observation in the open air, the angle-blocks remained warm after 

 the sides and the internal air had become cool, and a kind of mirage 

 was produced which distorted the image of a star into four long rays 

 like the sails of a windmill. M. Faye has particularly adverted to 

 this instance, and conceived that in the circumstances of our atmo- 

 sphere at the time of the eclij)se, where the air on one side only of 

 the path of light is somewhat heated by the sun, sufficient explana- 

 tion might be found for the distortion of some inequalities of the 

 moon. The Lecturer professed himself totally unable to follow this 

 theory into details, remarking only that in the rapid passage of the 

 moon's shadow he conceived it impossible to find air in the state 

 required for the explanation. 



The Lecturer then adverted to that part of his subject of which 

 all that had been already said was only introduc tory, namely the 

 approaching eclipse of July 28. After quoting an American news- 

 paper, showing the great interest excited by this eclips e beyond the 



