1864. ] The Royal Astronomical Society. 285 
Optical Effect of Atmospheric Refraction,’ which is, in fact, a reply 
to Mr. Airy’s. The latter observer, in his argument, assumed the 
effect of an atmosphere to be analogous to that of a convex lens, and on 
this assumption investigated the case mathematically. But Professor 
Challis contends that the courses of rays passing through a medium 
of variable density, like the atmosphere, cannot be similar to those 
passing through a convex lens; and that, therefore, in investigating 
the point at issue, respect must be had to the variation of the refractive 
index, in passing from one point of the medium to another. 
The Astronomer Royal has also contributed a few remarks on the 
amount of light given by the moon at the greatest stage of the 1863 
June 1 eclipse. As this eclipse, from the cloudless state of the sky, 
was very generally an object of observation, we give the Astronomer 
Royal’s remarks in full : — 
“The state of sky and of atmosphere was exceedingly favourable 
for observation of the lunar eclipse of last night. At the time of 
greatest obscuration, I carefully compared the light of the moon with 
that of several neighbouring stars. This I could do with considerable 
accuracy, by observing the objects with the eye unarmed, as my near- 
sightedness converts every object into a broad luminous disc, and there 
is no essential difference in the appearance of the moon and of a star, 
excepting in the quantity of light. In this manner I found that the 
light of the moon considerably exceeded that of Antares, sensibly 
exceeded that of Spica, and somewhat exceeded that of 2 Ophiuchi, but 
was a very little less than that of « Aquile. 
* Tt will be remarked that the moon’s centre was 22’ distant from 
the centre of the shadow at the time of conjunction in R.A., so that 
the moon was not very deeply plunged in the umbra. Had the eclipse 
been central, the light would have been much less.” 
We have to notice briefly the following papers, communicated at 
the meetings of November, December, and January; to which our 
limited space prevents our making a more lengthened reference :— 
F. Abbott, Esq., communicated some observations on the variable 
star 7 Argus. This same 7 Argus has been an object of scrutiny by 
other astronomers, and to whom it has caused some perplexity, and, 
amongst others, by Sir John Herschel, when at the Cape, with an 18- 
inch reflector. On that occasion, Sir John wrote in the following 
terms :—‘“ No part of this Nebula shows any sign of resolution into 
stars.” The form of the Nebula amongst which the star was situated is, 
as our readers are aware, figured in the ‘ Outlines of Astronomy’ in the 
shape of a dumb-bell, the star appearing of the first magnitude, and 
situated in its most dense part. It now seems that, although the star is 
in the dark space, out of the Nebula, which has altered in form, it only 
appears as a body of the sixth magnitude. These changes, both in 
Nebula and star, have taken place between 1858, the date of Sir John’s 
observations, and last year, when Mr. Abbott examined it. The 
author suggests that the variability of the star might be occasioned by 
the interference of the nebulosity surrounding it. 
A letter was read from Mr. Higgens, addressed to Admiral Smyth, 
