446 MR WILLIAM SWAN ON THE 
minence “ distinctly,” “ with its marked colour;”* and it was seen by so many 
persons at Goteborg, that its visibility to the naked eye was a common subject of 
conversation for some days after the eclipse. 
Mr Witttams observes, that “ the largest red prominence was visible by the 
unaided eye;”} and Mr Atry states, in his Account of the Total Eclipse of 1842, 
that an observer who accompanied him saw these objects with the naked eye.t 
The only observer of the late eclipse who formally states that he could not see 
the prominences without using a telescope, is Lieutenant Krac;) but such nega- 
tive evidence cannot affect the concurring testimony of so many observers who saw 
them distinctly by unaided vision; and we must therefore reject the idea that 
they are caused by the telescopes used in observing the eclipse. || 
2. On the Hypothesis that the Red Prominences are Phenomena arising from the Action of 
unequally heated Strata of Air on the Sun’s rays. 
Another opinion regarding the red prominences is that advanced by M. Faye, 
who conceives them to arise from a species of mirage, occasioned by the unequally 
heated state of the atmosphere during a total eclipse. The air all round the 
moon’s shadow is heated by the sun, while that within the shadow is sheltered 
from his rays. This he conceives occasions a reduction of temperature in the air 
within the shadow; and the warm air without, communicating its heat to that 
within, gives rise to a succession of concentric layers gradually decreasing in tem- 
perature, from the surface of the shadow inwards. These layers of unequal den- 
sity, acting on the rays proceeding from the edge of the moon to the observer’s 
eye, will, it is assumed,—like the unequally heated strata of air which sometimes 
exist near the horizon,—produce the well known phenomena of mirage. The red 
prominences, he supposes, are then merely the magnified and distorted images of 
lunar mountains, illuminated obliquely by the sun. 
* Edinburgh New Philosophical Journal, Oct. 1851, p. 375. 
+t Royal Ast. Soc. Notice, Jan. 1852, p. 54. 
t Royal Ast. Soc. Notice, for Nov. 1842, p.220. § Royal Ast. Soc. Notice, Jan. 1852, p. 47. 
|| M. Araco’s highly interesting Account of the Total Eclipse of July 1842, in the Anniaire 
for 1846, contains ample evidence of the visibility of the red prominences to the naked eye. The 
following are some of the testimonies to that fact. M. Araco says, “ A Perpignan, plusieurs per- 
sonnes virent les protubérances & Veil nu. Le fait n’est pas douteux.” (p. 412.) M. FLaucuercuss, 
who observed at Toulon, remarks, ‘“ Je n’avais point encore repris le télescope, lorsque je fus surpris 
par Vapparition d’wn point lumineux rouge; puis, d’un second point semblable.” (p. 418.) M. Sanrint, 
who observed the eclipse at Padua, relates that several persons saw the prominences with the naked 
eye, (p. 427.) 
I did not obtain access to M. Araco’s admirable Memoir until after this paper had been read ; 
otherwise I should have gladly availed myself more fully of its valuable contents than is now possible. 
eG Cette atmosphére conique [‘ le céne d’ombre’] doit produire, dans ses couches succes- 
sives, concentriques et de plus en plus froides, les phénoménes analogues aux réfractions qui s’opérent 
pres de V’horizon, en un mot, des phénoménes de mirage.” ‘“ Les montagnes roses qui apparurent alors 
[8 Juillet 1842], ne seraient autre chose que les images démesurément agrandies et déformées de 
quelques parties des montagnes lunaires, éclairées obliquement par le Soleil, et visibles 4 travers des 
vallées qui se trouvent ¢a et la, dans une direction favorable, sur le bord apparent de la Lune.”— 
Comptes Rendus de V Academie, 4 Nov. 1850, p. 643. 

