1851.] OF THE ROYAL INSTITUTION, 67 
taking the north limb to be the upper limb; that at 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 been seen of which one salient point might be the 
prominence in question. In all the places where the order of forma~- 
tion 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 different rooms of the same building at Padua. 
The determination of the locality and nature of these red pro- 
minences 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 along time, they 
underwent 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 ordinary mirage (the kind 
of reflection 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 
Observatory, when first mounted in a square pyramidal tube, whose an- 
gles were constructed more solidly than its sides, reducing the inner 
form to an octagon. When this tube had become warm before obser+ 
vation 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 pro- 
duced which distorted the image ofa star into four long rays like the 
sails of a windmill. M. Faye has particularly adverted to this in- 
stance, and conceived that in the circumstances of our atmosphere at 
the time of the eclipse, where the air on one side only of the path of 
light is somewhat heated by the sun, sufficient explanation 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 sha- 
dow 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 
