20 
which was sharply defined and distinct throughout, except at 
the ends of the arms, where its light gradually melted away. 
On looking through the numerous notices of paraselenz, which 
are to be found in the early volumes of the Philosophical 
Transactions, I find but one, seen by Hevelius at Dantzie, 
in the year 1660, which was similar to the present phenome- 
non, or to that of the preceding month described by Dr. Ro- 
binson. The non-appearance, in any instance, of a complete 
vertical circle, seems to forbid the supposition that this cross 
ean have been produced, like the horizontal white circle, by 
reflection from the facets of the prisms of ice. It is probably 
a phenomenon of diffraction ; and indeed it is described by one 
of the gentlemen who witnessed it, as resembling the cross of 
light which one sees, in looking at the sun or any bright ob- 
ject, through the silk of an umbrella. It would be impor- 
tant, with reference to the physical explanation of the pheno- 
mena, that the light, both of the horizontal circle and of the 
cross, should be analyzed with a tourmaline or double-refract- 
ing prism. The received explanation of the former may thus 
be easily tested ; for, it follows from the hypothesis upon which 
that explanation rests, that the light of the circle must be 
partially polarized in every part, the polarization increasing 
with the distance from the moon or sun on either side, up to 
a certain angle, at which it should be complete, and again 
diminishing from that point to 180° of distance, where it should 
disappear. 
A lunar halo, witha pair of false moons, similar to that above 
described, but without the cross, was seen at Bandon, in the 
County of Cork, on the night of the Ist of May. The appear- 
ances are thus described by Mr. Richard Allman: ‘* A faint 
halo surrounded the moon, at a distance which appeared equal 
to that of the pole star from the nearest point in the Plough. 
In this halo, at the extremities of the horizontal diameter, ap- 
peared two nebula-like, luminous masses, between which an 
intermittent stream of faint light seemed to play. I first per- 
