The parhelia Q R, were situated in a vertical plane pass ing through the eye at F, and the sun at G, in which ver tical the arches CR11, ORP either crossed or touched one another. These parhelia were sometimes brighter, some times fainter than the rest ; but were not so perfect in their. shape and whitish colour. They varied their magnitudes and colours, according to the different temperature of the sun's light at G, and the matter that received it at Q and R, and therefore their light and colours were almost always fluctuating, and continued as it were in a perpetual conflict. I took particular notice that they appeared almost the first and the last of all the parliclia, excepting that at N.
The altitude of Q above the horizon in the morning, at the beginning of the observation, was 49° 40' ; that of R was 76° 10'; that of the true sun was 28° 30'; hence the height of Q above the sun was 21° 10', and the height of R above the sun was 47° 40'.
" There was a north wind at the beginning of these ob servations, but by degrees it changed to the cast, and at last to the south; yet it brought no very great nor lasting rains. For near a fortnight after, the sky looked always vapourish ; and every day before dinner the sun endeavour ed to create new suns, but in vain, either for want of mat ter, or of a clue disposition. For in the vertical circle I saw plainly some sketches of parhelia for a long time. I saw also very manifest reciprocations of the lateral parhelia. The iris ORP seems to have been a portion of a single cir cle concentric to the sun, but towards X and 0 it did not quite touch the horizon AB; and the lengths of the arches Y, P B were variable. The arches Z Q a, p Q that immediately surrounded the sun, seemed to the eye to com pose a single circumference, but it was confused, and had unequal breadths ; nor did it constantly continue like itself, but was perpetually fluctuating. But in reality it consisted of the arches expressed in the scheme, as I accurately ob served for that very purpose. The horns HRC seemed to be a portion of a smaller circle, touching the grt ater ORP in a contrary position in a common knot at R. The arches cut each other in a knot at Q, and there they' formed a par helion. The parhelia N, M, sprung out from the com mon intersections M, N of the iris and of the whitish circle ONMP. The north part of the sky was clearer than the south, which being overcast with slender vapours, af forded more matter for this appearance." See Gassendi's Opera, tom. vi. p. 401.
Hevelius observed the following paraselenm at Dantzic on the 30th March 1660. " In the beginning, at one o'clock in the morning, the moon A was surrounded by an entire whitish circle BODE, in which there were two mock moons at B and D, one at each side of the moon, con sisting of various colours, and shooting out very long and whitish beams by fits. That on the left hand extended its tail towards the thigh of Scrpentarius, the other on the right extended its tail towards Jupiter, as represented in Fig. 4. Afterwards, at two o'clock, a larger circle surrounded the lesser, and reached down to the horizon. The tops of both these circles were touched by coloured arches like invert ed rainbows. The inferior arch at C was a portion of a larger circle, and the superior a portion of a lesser. This extraordinary sight lasted near three hours ; the out ward great circle vanished first of all, then the larger in verted arch at C, and presently the lesser, and, last of all, the inner circle BCDE disappeared. The diameter of this inner circle, and also of the superior arch, was 45 degrees; that of the exterior circle, and inferior arch, was 9U de gr ees." On the 6th April 1660 Hevelius observed the parhelia shewn in Fig. 5. " At half an hour past live in the evening, while the sun was descending towards the horizon, he was crowned with arches of circles of various colours like the rain-bow. In the corona, on opposite sides of the sun, there were two parhelia, variously coloured with pretty long and whitish tails pointing from the sun. Near the zenith, where the corona was a little faint and imperfect, there shone out another inverted arch, having a third par helical in the middle of it, which appeared somewhat ob scure. This phenomenon lasted half an hour till sun-set, the sun being very clear. The inverted arch, and the upper parhelion, disappear ed first ; and then the parhelion on the left hand ; but the third parhelion set with the true sun. The diameter of the corona round about the sun was about 45 degrees, as I guessed by my eye." On the 17th December 1660, Hevelius observed at Dant zic, the following paraselcirm, which are shewn in Fig. 6. " On the first day after the full moon," says he, " at thirty minutes past six in the morning, the moon being 12° high, I saw the moon in the west, with three mock moons about her in this manner. The air being very clear at first, I ob served the moon surrounded with a double corona (near her body, as the figure seems to represent) tinged with very bright and beautiful colours. On each side of the
moon there were .two arches of a large circle, about 45 de grees in diameter, which were also coloured like the rain bow, and extended down to the horizon, in which were two mock moons with very long white tails. That on the left hand was near Procyon with a short tail ; the other on the right hand had a longer tail. In the upper part, where these collateral arches concurred, there was another arch inverted and variously coloured, with a third mock moon in the middle of it, and somewhat duller than the other two. Moreover, what was very extraordinary, there passed a large white rectangular cross through the middle of the moon, whose lower part reached down to the horizon; but on each side it did not quite touch the corona, as appears by the figure. It was so very bright and strong; that it shone distinctly and clearly till sun-rise; but the mock moons disappeared a little before." In Mathew Paris's History, the phenomenon seen in Fig. 7. is thus described : " A wonderful sight was seen in England, A. D. 1233, April 8, in the 17th year of the reign of Henry III. and lasted from sun-rise till noon. At the same time, on the 8th of April, about one o'clock, on the *orders of Herefordshire and Worcestershire, besides the true sun, there appeared in the sky four mock suns of a red colour ; also a certain large circle of the colour of crys tal, about two feet broad, which encompassed all England as it were. There next went semicircles from the side of it, in whose intersections the four mock suns were situated; the true sun being in the east, and the air very clear. And because this monstrous prodigy cannot be described by words, I have represented it by a scheme that shears im mediately how the heavens were circled. The appearance was painted in this manner by many people, for the wonder ful novelty of it." Figure 8. represents a parhelion observed at Leyden, A. D. 1653, Jan. 14, between one and two o'clock in the afternoon, in the academical observatory, by Samuel Char. Kechelius a Hollenstein. " The circle BDC was white, and almost 35' broad; the altitude of its highest point D was 23'. Its centre was in the sun, whose height was 48'; that is, at 36' past one, his azimuth being 23° 40' to wards the'west, and the angle made by his vertical circle and the ecliptic 60° 54'. The mock suns 13, C were oblong and unequal, at the distance of 22° 35' on each side of the sun, and had the same altitudes as the sun. The western parhelion at C was the fainter of the two, and changed from yellow to white, and disappeared first ; the eastern one at B was brighter, with a lucid arch shooting from the sun, and was coloured with purple, red, and yellow ; the shape of its tail OF was conical, 27° long, the parhelion be ing the base of the cone; the part BE, 13' It/ long, consist ed of bright yellow, and red light; the other part El? being whitish, which vanished before the parhclion did. It ap peared for hall an hour, and lasted one quarter longer than C ; and the corona disappeared a little after." On the 13th May, 1652, Huygens observed a halo, which he thus describes observed a circle about the sun in its centre; its diameter was about 46°, and its breadth the same as that of a common rain-bow. It had also the same colours, though very weak, and scarce discernible but in a contrary order, the red being next the sun, and the blue being very dilute and whitish. All the space within the circle was possessed by a duller vapour than the rest of the air, of such a texture as to obsetti;e the sky with a sort of a continued cloud ; but so thin, that the blue sky colour appeared through it. The wind blew very gently front the north." On the 8th of April, 1702, Dr Halley observed a halo with parhelia, and tangent arches, as shewn in Fig. 9. where S is the sun, Z the zenith, STPP a large white circle passing through the sun, and nearly parallel to the horizon. It was about 2° broad in the northern part about 1', and continued of the same breadth in the east and west; but grew narrower towards 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 extra ordinary sight. The halo VXNY was 22° in diameter, the red rays being nearest to the sun. The arch PVP had its centre 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 311°. Another arch appeared at N, having its centre about V. The height of the sun during the obsOrvation 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. Trans. 1702, vol. xxiii. No, 278, p. 1127.