510 PROFESSOR PIAZZI SMYTH ON THE 
result was obtained when a circular plate was made to eclipse the sun’s image in 
the focus of the telescope, and I looked directly into the eyepiece. But hardly 
any other result could well be expected, as however dark the room might be 
kept by the apparatus employed, that in no wise checked the illumination of the 
atmosphere outside, in the apparent neighbourhood of the sun, the daylight, in 
fact; and this was always so bright, that no object of the reputed faintness of 
these red prominences could well appear on so luminous a background. 
There is only one way of getting over this difficulty; 7. ¢., taking the telescope 
to the top of a high mountain, above all grosser parts of the atmosphere. Other 
circumstances have lately compelled me to request leave from Government to 
take the Edinburgh Equatorial temporarily to the top of the Peak of Teneriffe; and 
if allowed to do so, it shall be one of my first cares to repeat this experiment. 
This mode undoubtedly would not be perfect, none would unless tried alto- 
gether above the limits of the atmosphere; but it would certainly be a great im- 
provement on anything done on the surface of the earth at the level of the sea, 
and might perhaps be found sufficient for the object in view. All travellers who 
have ascended high mountains, combine in speaking of the greater blackness of 
the sky witnessed in those elevated regions, as well as of the sun becoming 
more luminous and more concentrated as to his rays, and of stars becoming 
visible to the naked eye by day. Captain Hopexs, at the height of 15,000 feet 
on the Himalayas, saw, with a two-inch object-glass, stars of the fifth magnitude 
in the open sunshine: but onthe Calton Hill, with the smoke of Edinburgh more 
or less diffused through the air, stars of the first magnitude are frequently in- 
visible, in our pale blue sky, to a six-inch object-glass; thus making a difference 
in favour of the mountain station, of at least 100 to 1. I have not myself had 
experience of such great heights, but have observed for months at the altitude 
of 6000 feet, and from the improvement in the transparency of the atmosphere 
up to that point, can well believe what has been related of the higher station. 
Thus far I have gone on the supposition that it was right and proper to attach 
great importance to the conclusions of the actual observers, that the red promi- 
nences were actual material bodies. This, however, has not been proved; and 
we cannot be too careful in guarding against the deceptive effects of objects close 
by. Now it is not difficult to suppose some partial diffractions of the sun’s light 
amongst the craggy mountains of the moon, during the total eclipse, which might 
make some rays diverge, and become visible in an anomalous manner. Accord- 
ingly, I introduced into the focus of the object-glass a small sphere, which was 
made to pass before and so eclipse the sun’s image, as in the natural pheno- - 
g p 
menon. 
The results were, that light of a pink colour was thrown off from the edge of 
the sphere, and in greater quantity as the polish of the surface was higher; in a 
complete ring if the surface was smooth, and in detached portions if the surface 
9 ge a rs ay 
