
RED PROMINENCES SEEN DURING TOTAL ECLIPSES OF THE SUN. 449 
3. On the Hypothesis which would refer the Phenomenon of the Red Prominences to the 
Action of the Moon’s Limb on the Sun’s Rays. 
If we suppose the prominences to be caused by some action of the moon’s limb 
on the rays of light, whatever hypothesis we form regarding the precise nature of 
that action, it is evident, that the effect produced will depend in some way upon 
the relative positions of the luminous object,—of the body acting on its light,—and 
of the observer's eye. Any change in the position of the observer relatively to 
the sun and moon, would seem to necessitate some change in the appearance of 
the red prominences, supposing them optical phenomena of the nature of reflexion 
or diffraction; and these are the only known species of phenomena which the 
action of the moon’s limb on the sun’s light would occasion. 
Now, as the moon and earth are in rapid motion, the position of an observer 
relatively to the line joining their centres is continually changing; and in order 
to see the supposed optical phenomena always from the same point of view, it 
would literally become necessary for him to run a race with the moon’s shadow. 
It thus seems difficult to avoid the conclusion, that if the red prominences 
were caused by the action of the moon’s limb on the sun’s light, their appearance 
should rapidly change during the progress of the eclipse. But it has already been 
seen, that their forms remained unaltered; and it is therefore in the last degree 
improbable that they are optical phenomena, caused by the action of the moon’s 
limb on the sun’s light. 
Il. On the Hypothesis that the Red Prominences exist in the Sun or Moon. 
On these grounds it seems impossible to regard the prominences as mere 
optical phenomena. Let us now inquire whether equal difficulties attend the sup- 
position that they are objects really existing in the sun or moon. 
1. On the Discrepancies in the Observed Positions of the Red Prominences. 
The observers of the late eclipse seem frequently to have adopted no better 
means of ascertaining the angles of position of the red prominences, than estima- 
tion by the eye, with reference either to the sun’s vertex or north point; and in 
many cases the point of reference is confessedly only roughly estimated. In some 
instances also, the angles have been merely guessed by the editor of the Royal 
Astronomical Society’s Transactions, from the drawings furnished by the ob- 
servers ;* and in such circumstances, we may be prepared to expect notable dis- 
crepancies in the observations. 
In other cases, however, greater care was taken to ensure accuracy. ‘Thus Mr 
Dawes observed the eclipse with a telescope equatorially mounted, having cross 
* Royal Ast. Soc. Notice, p. 43. 
VOL XX. PART III. 65 
