234 Proceedings of Metropolitan Societies. | April, 
been making experiments with it, in the unsilvered state, wpon celes- 
tial objects, with the view of ascertaining how far a diminution of light 
and consequently of the evils of irradiation, combined with a large 
aperture, might be of advantage in particular cases. For this purpose, 
on the 20th of September, at about 6 p.m, before the sun had set, t 
turned the telescope upon the moon, then a few hours past her first 
quarter. I had no sooner focussed the telescope (power 120) than I was 
astounded at observing that the limb of the moon was entirely out of 
shape; that it was, in fact, irregularly polygonal, as if several large 
segments had been cut off the spherical limb—not the terminator.” 
Upon observing these remarkable appearances the author wrote to 
his friend, Mr. Webb, who, on examination. at once detected them ; and 
proved their existence beyond a doubt by the use of the wire of the 
micrometer. Subsequently, September 25th, when Mr. Key again ex- 
amined the limb he was only able to trace a very faint appearance of 
a depression. From this circumstance the author is led to believe that 
the maximum visibility of these depressions only lasts for a short 
period; and that the effect of irrad‘ation would render their detection in 
ordinary instruments extremely difficult. 
Now that this extraordinary phenomenon has been once discovered, 
it is to be hoped that observers will direct their attention to so interest- 
ing a subject, and will provide themselves with instruments calculated 
to exhibit more perfectly the true form of the limb. For this object 
Mr. Key strongly urges the adoption of the plain, in addition to the 
silvered speculum. We should state that the drawing was made from 
memory the following day, and although it but represents roughly the 
positions of the depressions, he does not consider them exaggerated. 
The deepest depression below the surface of the moon he estimates at 
about 25 miles. 
A paper, “ On the Origin of the apparent Luminous Band which, in par- 
tial Eclipses of the Sun, has been seen to surround the Visible Portion of the 
Moon’s Limb,” was communicated to the Society by G. B. Airy, Astro- 
nomer Royal. The object of this paper was “to show, by optical 
investigation, that no refraction can cause a change in the apparent 
brightness of the surface viewed.” As the paper was necessarily of a 
purely mathematical character, we shall content ourselves with merely 
giving our readers its general results. Having arrived, from this 
treatment of the subject, at the conclusion that ‘ refraction by a lunar 
atmosphere cannot explain the more luminous band which appears to 
surround the moon’s limb where it crosses the sun’s disc,” the author 
goes on to state his opinions on its real origin in very positive terms : 
‘‘T have. no difficulty in explaining to myself the origin of the luminous 
band in question. It is strictly an ocular nervous phenomenon ; not 
properly subjective, but sensational—a mere effect of contrast. I have 
seen it so frequently under circumstances very different from these, 
that I cannot have the smallest doubt on the matter.” 
In this paper the author entertains views antagonistic to those 
previously expressed by Professor Challis, in a paper contained in the 
‘Monthly Notice, June 12, 1863, and at the mecting in January last 
Professor Challis communicated a paper “ On the Calculation of an 
