548 Froceedings of the Royal Irish Academy. 
L. — On an Inverted Lunar Halo, and a Lttnae Rainbow. 
By Henry Hennesst, F.R.iS., M.KI.A. 
[Read December 8, 1873.] 
On the night of Sunday, December 15, 1872, a short time before 10 
P.M., I noticed a faint white circular arch, not far above the horizon, 
to the N.JS'.W., and directly opposite to the moon's place. It was pro- 
bably about 70° from the moon, and had its concave side upwards, as 
represented in Plate xxxiii."^' It was decidedly eccentric to the moon, and 
could not come within the class of any of the ordinary halos, of 
which the maximum diameter, passing through the moon, would 
be 90°, and therefore the distance of a part of the luminous circle 
45°. This diameter is one, moreover, very rarely seen, and from 
the appearance of the luminous arch here described, its diameter could 
not exceed 45°. The moon was at this time 15 days old, and very 
near the zenith, from which it was shining brightly on the light clouds 
in the direction of the luminous arch, although it was partially ob- 
scured itself behind a cloud which covered its disc. 
The position of this arch with reference to the moon, namely, with 
its concavity turned towards the luminary, shows that it belongs to the 
class of halos, and notwithstanding its distance, it could not be consi- 
dered as a lunar rainbow. It was totally unlike the very remarkable 
halo described in the Proceedings of the Academy, vol. iii. p. 18, by 
the Eev. Provost Lloyd and Mr. Clibborn ; nor can I find a descrip- 
tion of anything precisely similar on consulting the writings of many 
other observers of such phenomena. Dr. Lloyd remarks in his paper, 
that it would be interesting to multiply the records of such phenomena, 
so as to be able to trace the extent and limits of the cloud near the 
moon's place, in connexion with which halos are usually observed. As 
in this case the cloud which exhibited the phenomenon was distant 
from the moon, all the facts of the case show that it could arise only 
from a peculiar refraction, accompanied by some reflection, of the lumi- 
nous rays, which it is not easy to trace with precision in the absence 
of exact angular measurements. 
In order to trace the connexion, if any, between this phenomenon 
and the state of the weather at the time it was observed, I consulted 
the records of the Observatory at the Phoenix Park, as published by 
the Eegistrar-General, with the following results: — 
The portions dotted represent the outline of the halo, if it -were complete. 
