243 
SCIENTIFIC SUMMARY. 
ASTRONOMY. 
Atmosphere of Sun , Planets , fyc . — Professor Challis accounts for the 
bright band bordering the edge of the moon during solar eclipses 
(which was noticed by Professor Alexander in 1831 and 1860, and which 
is likewise depicted in Mr. de la Rue’s photographs) to the refraction 
caused by the atmosphere of the moon. At the November meeting of the 
Astronomical Society, the Astronomer Royal read a paper, in which his 
object was to prove that no refraction could cause a change in the appa- 
rent brightness of the surface of the sun bordering on the moon’s edge. 
He is of opinion that this luminous band arises from a mere effect of con- 
trast, and that it is an ocular nervous phenomenon. As an instance of 
this, he states that if a piece of black cloth is swung between the eye and 
a moderately-illuminated whitish wall, that the edge of the cloth will be 
preceded by a broad luminous band. From the decay of the irritability of 
the retina, it is not so well seen by him now as formerly, when, on favour- 
able occasions, its angular breadth was not less than two degrees. In 
regard to the eye-view of the photographs of the eclipse, it is stated that 
the explanation of the Astronomer Royal has been confirmed by some 
experiments made by Mr. de la Rue. 
Depressions on the Lunar Surface . — On September 20, at 6 p.m., the 
Rev. IT. C. Key, on looking at the moon with a 12-inch glass speculum, 
noticed that its edge did not present the usual circular form, but that it 
was quite out of shape ; in fact, irregularly polygonal. Four sides, or 
plains, were distinctly seen on the illuminated limb. They could not be 
seen with the same telescope on September 25, but were observed by the 
Rev. T. W. Webb on September 30. Mr. Key is of opinion that they are 
not visible for more than forty-eight hours at a time, and that the best 
time for viewing them is from three to four da}^s after the greatest south- 
east libration. The largest of the plains stretched over more than thirty- 
five degrees of latitude, and its deepest depression below the general level 
was estimated at twenty-five miles at the least. These observations were 
made by the glass speculum in an unsilvered state, and Mr. Key strongly 
recommends its use in this condition, not only in regard to the sun, but 
with the planets, especially Venus. The delicate pencilling on the surface 
of Jupiter was brought out with marvellous effect, and Saturn appeared 
as if seen in relief, the body of the planet seeming to be isolated and 
suspended within the rings. From the total absence of irradiation he 
likewise recommends this plan for observing occultations by the moon, as 
well as the moon itself. When at the time of new moon the whole peri- 
phery is seen, the effect of this irradiation is very apparent, the illuminated 
edge appearing to be a portion of a much larger circle than the rest. 
