__ ‘but so thin, that the blue sky colour. red through 
ag The wind blew very a from the north.” 
by halo with parhelia, and tt arches, as shewn in 
Fig. 9. where S is the sun, Z the zenith, STPP a large 
vb circle passing through the sun, and nearly pa- 
® —_xallel to the horizon. It was about 2° broad in the 
EXXXVII northern part about T, and continued of the same 
breadth in the east and west ; but grew narrower to- 
wards the sun, Its edges were not very well defined, 
and the whole circle, seen on the pure azure sky, was 
considered by Dr Halley as a very extraordinary sight. 
The halo VXNY was 22° in diameter, the red rays 
being nearest to the sun. The arch PVP had its cen- 
tre nearly at N; and at its intersections P, P with the 
large white circle, there were two. bright parhelia 
tinged with colours, The distance PS was 314°.. An- 
other arch appeared at N, having its centre about. V. 
The height of the sun during the observation was from 
40° to 45°. The weather was cooler than ordinary, 
and the vapour which produced the phenomena was 
higher than the clouds; for they were seen to drive 
under the circles. See Phil. Lrans. 1702, vol. xxiii, 
, ae, 278, p. 1127. , 
seen A very curious halo, with its accompanying pheno- 
mH mena, was seen by Mr Barker on the 22d 9k anand 
vdesg 1771, a little before two o'clock, at Fort Gloucester, on 
71, the river of Lake Superior. The weather was extremely 
cold. ‘ There was a very large circle, or halo, round 
the sun, within which the sky was thick and dusky, 
_._»» the rest of the hemisphere being clear, and alittle more 
_ ««» than half way from the horizon to the zenith, was a beau- 
tifully salightened circle parallel to the horizon, which 
went quite round, till the two ends of it terminated in 
the circle that surrounded the sun, where, at the points 
of.intersection, they each formed a luminous appearance 
about -~ size of the sun, and ae like mag when seen 
a thick hazy sky, that they might very easily 
ree aa taken for him, Directly opposite to the sun 
was a luminous cross, in the shape of a St. Andrew’s 
eross, cutting at the point of intersection the horizontal 
circle, where was formed another mock sun like the 
other two. The two lower limbs of the cross appeared 
but faintly, a little way below the circle. The, two 
i reached.a good way above the circle towards the 
zenith, very. clear and bright, In this horizontal cir 
cle, directly half way between the sun and the cross; 
and those at the ends of the same circle, were other two 
mock suns of the same kind and size, one on each side; 
so that in this horizontal circle were five mock suns at 
equal distances from each other, and in the same line 
‘ the real sun, all at equal heights from the horizon. Be- 
$7 sides these meteors, there was very near the zenith, but 
7 a little more towards the circle of the real sun, a rain- 
bow of very bright and: beautiful colours, not an, entire 
semicircle, with the middle of the convex side turned 
towards the sun, which lowered as the sun descended, 
‘This phenomena continued: in all its beauty and lustre 
‘tillabout half after two. The cross went ually off 
first, then the horizontal circle began to A yc 
“parts, while in. others it was visible; then the three 
»mock.suns farthest from. the sun, the, two in the sun’s 
_ circle. continuing longest; the rainbow began to de- 
4 -erease after-these, and last of all the sun’s.circle ; but it 
+ 
was observable at three o'clock or after it. See Phil. 
» Trans. 1787; vol. xxvii. p. 440. 
&e.. +On the 15th June 1790, a complicated system of 
®Y halos and parhelia was observed at St Petersburg by 
' M. Lowitz.. They are represented in Fig. 10, The 
lo, axehes A, B,and C were coloured, and, like all the other 
HALO. 
On the Sth of April, 1702, Dr Halley observed a - 
615 
coloured parts, had the red towards the sun. Twoan- Halo. 
thelia appeared at D-and E. _—— 
A curious halo, observed by Mr Hall in Berwick Halo obsers 
shire, on the 18th of February 1796, about 10 o'clack, ved by Mr 
is shewn in Fig. 11. ‘The moon was about south-west, 1!) a 
and the altitude of her limb nearly 54°, The diameter } . 
of the great halo was about 112°; and that of the small COLXXxVEr 
0, having the moon in its centre, was-between 8° and Fig. 11. 
12°. The weather was remarkably mild, and there was 
little or no wind. 
On the 20th of November 1802, at 2 o'clock, Sir Hen- Halos ob- 
ry Englefield observed at Richmond in Surry, two wn- served by 
common halos and parhelia, The altitude of the sun Sir H. Ens 
was 14°, The circle nearest the sun(Fig. 12.) was about $'*feld 
24° distantfrom him, and about a degree broad. Its light Fi = 
was a pale yellow, without any of nagaignadia colours.” 
The exterior circle was 48° from the sun, and about 14° 
broad. It was tinged with the prismatic colours, the 
red being nearest the sun, In the left branch of the in- 
ner circle, in a line parallel to the horizon, and passing 
through the sun, was a very faint parhelion ; but in the 
upper point of the same circle was a very remarkable 
one, Its light was so vivid that it could scarcely be 
viewed, pee it was rather brighter than the real sun. 
“ It was of a whiter light than the rest of the circle in 
which it was, and had a pearly appearance, as partaking 
a little of prismatic tints. It was large, perhaps in its 
brightest part near 2° broad, very ill defined every where, 
but most diffused. in the part farthest from the sun. 
From each side of the bright light proceeded.a bright 
ray, which had a double curvature very distinct, being 
first convex towards the sun, and then concave. The 
lower edge of these rays (or that nearest the sun) was 
tolerably well defined; the upper edge melted away 
into the sky with a sort of streakiness. They grew both 
narrower and fainter towards their termination, and 
they reached pretty near tothe other circle. The whole 
form of this parhelion and its rays bore so striking a si~ 
militude to the body and. extended wingp of a long 
winged bird; such as am eagle, hovering directly over 
the sun, that superstition would really. have. had little 
to add to the image.” See the Journals of the Royal 
Institution, vol. ii. or Nicholson’s Journal, vol. vi. p.d4- 
Acoloured drawing of this phenomenon, will be found in 
Dr Thomas Young's Natural Philosophy, vol i, plate- 
xxix, Fig. 431, 
Having thus given a description of some of the most 
interesting halos and parheliathat have been accu- 
rately observed, we shall now proceed to give some ac- 
count of the theories by which these phenomena have 
 eenaie eae hak ted by th 
escartes su { halos are genera ythe,.. 
rays of the sec ad achanl through flat stars of pellucid mac ‘ 
ice ; but-it follows from this supposition, that the space . 
within the halo should appear brighter than that with- 
out, which is-contrary to observation, See Descartes, 
Met Cap. x. F ‘ 
The subject of halos was next investigated by Huy opinion uf 
gens, who published a large dissertation concerning Huygens. 
their cause, which has been translated and,reprint 
by Dr Smith, in his Treatise on Oplics.. Huygens 
assumes the existence of particles of hail, some of which 
are globular, and others cylindrical,, with an opaque 
portion in the middle of each, bearing a certain. pro- 
portion to the whole; and he supposes these cylinders 
to be kept in a vertical position by a current of ascend- 
ing air or vapours, and sometimes to have a position in- 
clined to the horizon in all directions when they are 
dispersed by the wind or otherwise, The cylinders are 
Th of” 
hala? 
