TOTAL ECLIPSE OF THE SUN, JULY 28, 1851. 3435 
































q - granite mountains. Both prominences were remarkably distinct from the co- 
'* rona, so as almost to appear standing in front of it; and their outlines seen 
' upon it were at least as definite as that of the illuminated edge of a detached 
cumulous cloud projected against the clear blue sky. But as the sharp definition 
of such a cloud is an illusion, depending as much on its distance, as on the density 
of the vapour composing it, I do not mean to draw from this comparison any 
_ inference regarding the density of the matter composing the red. prominences. 
Notwithstanding their definite outlines, they may, like the tails of comets, be of 
extreme rarity, and indeed, as Sir Jonn Herscuen remarks,* their faint illumi- 
nation clearly proves them to be “cloudy masses of the most excessive tenuity.” 
The colour of the prominences was a full rose-tint, and the light of the corona in 
their neighbourhood seemed brighter than elsewhere, with the exception of the 
brilliant beams already mentioned. i 
The appearance of the prominences as they were seen shortly after the com- 
mencement of the totality is represented in figure 7. By means of the microme- 
ter I determined their positions as well as that of the bright rays to the east of the 
sun’s vertex, and then quitted the telescope for a little to make some other ober- 
vations. Onreturning to the telescope I found that the bright rays to the east of the 
sun’s vertex appeared shorter than before, while the red prominences to the west 
had increased sensibly in height; and while I watched them, they continued to 
increase still more in size, as if rising from behind the moon’s limb. I should 
almost say their motion was sensible; but however doubtful this may be, its 
cumulative effect was strikingly apparent, for before the end of the totality they 
had assumed the appearance presented in figure 8. All this was exactly what 
would have happened on the supposition that the prominences belonged to the 
sun ; for objects on the eastern limb would gradually suffer occultation by the ad- 
_ yancing moon, while those on the western limb would be simultaneously exposed. 
While, then, the definite outlines and permanent forms of the prominences 
_ satisfied me that they were real objects, and not mere optical phenomena, their 
_ gradually increasing altitude convinced me that they belong to the sun and not 
_ tothe moon. The observed angles of position of the red prominences and spots 
on the sun’s disc, referred to the sun’s vertex, and also their angles of position 
_ reckoned eastward from the sun’s vertex are given in Table IL, p. 346. The data 
for reducing their positions to the sun’s vertex are the known latitude of the 
station, the sun’s declination, and the hour angle from apparent noon, assuming 
the observations to be made at the middle of the totality. 
The prominences were distinctly visible to the naked eye by the strong red 
tinge they imparted to the adjacent portions of the corona; but I could neither 
distinguish their outlines nor see them as separate objects. 
I wished to compare the shadow cast by the corona with that formed by a 
-* Outlines of Astronomy, 1851, par. 395. 
VOL. XX. PART III. 5A 
