246 Proceedings of the Royal Irish Academy. 
XXYIII. — ISToTEs OF Obseevatiojsts op Phen-omena in Optical Meteor- 
ology. Ey Henry Hennessy, E. E,. S., Y. P. K. I. A. 
[Read January 8, 1872.] 
In the Athenseiim " for March, 1866, 1 described a solar halo, which 
was accompanied by meteorological phenomena of a remarkable kind. 
I now present brief notes of similar optical appearances more recently 
observed, partly because of the comparative rarity of one or two, but 
chiefly on account of their probable connexion and dependence upon 
more important phenomena. 
On November 20th, 1869, at 10 p. m., I observed a lunar halo 
of 45° in diameter. It continued visible until midnight. At the 
time, the air was changing from a dry, cold condition to one of damp- 
ness and higher temperature. The barometer fell nearly one inch 
between the 21st and 22nd of JN'ovember, and it is apparent that the 
halo was due to snow crystals which were forming in the upper cold 
strata of air, by the condensation of the vapour transferred thither by 
a current blowing from the S. W. 
During the afternoon of July 10th, 1871, there were many heavy 
showers, accompanied by thunder and lightning, in the Bay of 
Dublin. Immediately after one of these showers, at 7 p. m., I ob- 
served, from Merrion, a well-developed double rainbow stretching 
from Howth to Killiney. Before the secondary bow had become dis- 
tinctly visible, I noticed a perfectly straight vertical column of light 
nearly tangent to the primary bow at its north side, as delineated in 
the accompanying sketch. 
It presented faint prismatic colours, in the same order as the 
rainbow — namely, violet inside and red outside — and its straightness 
