Mr. Airy on the Total Solar Eclipse of July 8, 1842. 395 
to the sun’s limb, and cover it. In other words, I saw the totality 
completed twice. With regard to the fact, I can only say that I 
was at the time most fully alive to everything which occurred, and 
that I was specially prepared for an observation which I expected to 
be one of the most important in the whole eclipse ; and I have not 
the smallest doubt that the thing occurred, under the circumstances 
in which it was viewed with my telescope, precisely as I have stated. 
The explanation I cannot offer with great confidence, but I conceive 
that it may be the following. I have already remarked, that the 
light of the sun’s disc, very near to its limb, is considerably less 
than in those parts of the disc which are a little further from the 
limb. This being assumed, it is evident that the interference of a 
cloud, which was sufficiently dense to hide the faintest part of the 
disc (at the limb), but not sufficiently dense to hide the brighter 
parts, would sensibly diminish the sun’s diameter. Now I was as- 
sured by my companion that there was a cloud upon the sun at the 
time when I first saw its extinction; and this cloud, though not 
sufficient to conceal the edge of the sun’s disc from the naked eye, 
might be sufficient to conceal it as viewed in a telescope, in which 
the specific brightness of any surface is much less than to the naked 
eye, and which also was armed with a dark glass. But if this ex- 
planation is valid, it may apply to many other phenomena. I have 
frequently seen the sun’s limb deeply notched, and I have conceived 
that this was due to irregularity of refraction; it may have been due 
to irregularity in the transparency of the atmosphere. Mr. Baily’s 
beads may themselves have depended on this circumstance. I now 
return to my narrative. 
I saw nothing whatever of beads, or other irregularity, in either 
of the extinctions of the sun’s limb. The cusps were perfectly well 
defined till they met. 
I quitted the telescope and looked round the horizon. The out- 
lines of the mountains could with great difficulty be seen. But 
everything, though not black, appeared horribly gloomy. My com- 
panion believed that there was a dark green tinge on every object. 
I did not remark it. I endeavoured to ascertain whether the dark- 
ness could be seen sensibly to travel over the great plain, but could 
not satisfy myself that it was so; the whole seemed to me to be- 
come dark at once. Professors Plana and Forbes, however, on the 
Turin observatory, (from which the mountains to the north and west 
are visible, but not the plain,) were confident that they saw the 
darkness travel gradually. It is possible that from my elevated po- 
sition I saw the country too much in detail to observe this; it is 
possible, also, that my eye was applied to the telescope at the cri- 
tical time. The illumination was so small, that I could with diffi- 
culty read the divisions on the watch-plate, which was within eight 
inches of my eye; I did not try a printed book. The clouds were 
much less distinct than before, but as far as they could be seen they 
appeared terribly threatening. But the appearance of the moon can 
never be forgotten. It was like a black patch fixed in the sky, sur- 
rounded by a ring of faint light, er breadth I estimated at jth 
2D2 
