« ZurückWeiter »
Tuo Mock-Suns, and an Arc of a Rain.bow inverted, with .
By the Rev. William Whiston.
ABOUT ten o'clock in the morning, on Sunday Oct. 22, 1721, being at Lyndon, in the county of Rutland, after aurora borealis the night before, wind W.S.W. I saw an attempt towards two mock. suns, as I had done sometimes formerly. About half or three quarters of an hour after, I found the appearance complete ; when two plain parhelia, or mock-suns, appeared tolerably bright and distinct; and that in the usual places, viz. in the two intersections of a strong and large portion of a halo, with an imaginary circle, parallel to the horizon, passing through the true sun. This circle I call imaginary, because it was not itself visible, as it sometimes has been at such appearances. Each parhelion had its tail of a white colour, and in direct opposition to the true sun ; that to. wards the east was 20 or 25° long; that towards the west about ten or twelve degrees; but both narrowest at the remote ends. The mock-suns were evidently red towards the sun, but pale or whitish at the opposite sides, as was the halo also. Looking upward, we saw an arc of a curious inverted rainbow, about the middle of the distance between the top of the halo and the vertex. This arc was as distinct in its colours as the common rainbow; and of the same breadth. The red colour was on the convex, and the blue on the concave of the arc ; which seemed to be about 90° long : its centre in or near the vertex. On the top of the halo was a kind of in. verted bright are, though its bend was not plain. The lower part of the halo was among the vapours of the horizon, and not visible. The angles, as more exactly measured on Monday, near noon, when the same appearance returned again, but more faintly, were as follow: the sun's altitude 22°; perpendicular semidiameter of the halo 23} ; distance of the rainbow from the top of the halo 231°; semidiameter of the arc of the rainbow, if our vertes be gupposed its centre, 21°. The phenomenon lasted each day for an hour and a half, or two hours. What was most remarkable on Monday was, that the wind, which on Sunday had been almost in.
sensible, was now become sensible, and changed to N.N.E. that the halo was sensibly become oval; its shorter axis parallel to the horizon; and the two mock-suns, which were then but just visible, especially that on the east, were not in the halo, but a degree or two without it, which I ascribe to the unusual shortness of the ho. rizontal diameter; which position of the mock-suns does not appear to have been hitherto taken notice of by any, though it was now very sensible.
October 26, about nine in the morning, as I was coming in the Northampton coach towards London, the halo returned larger and clearer than before ; and the two mock-suns just attempted an appearance, as on Sunday ; but the air becoming thicker and thicker towards rain, I saw them no more. I add nothing to this account, but only, that August 30, before, I saw at the same place, Rutland, a remarkable halo, whose upper part had its inverted arc reddish within, and pale without, but brighter and more vivid than ever I saw before. That we had there, September 11, in the evening, the lightest and most remarkable aurora borealis, with its unaccountable motions and removals, that ever I saw, excepting that original one, March 6, 1711: that it was seen in Northamptonshire, at the Bath, and elsewhere: that the vertex of the co. Jumns which shot upwards, was not our vertex, but evidently fifteen or twenty degrees distant towards the south; and that the wind was in Rutland north, as I observed myself; at the Bath west; and in Northamptonshire south ; all at the same time, which deserves particular reflection.
January 13, 1768, between nine and ten in the morning, being on an eminence that overlooked some low meadow ground, Mr. Cochia observed, in a direction opposite to that of the sun, which shone very bright, and in a mist which covered the said inclosures, an unusual meteor, which, without attempting to name it, be describes by help of the above figure. At about the distance of half a mile, and incurvated towards each other, like the lower ends of the common rainbow, there appeared in the mist two places of a peculiar brightness, as represented at A A. They seemed, as is common, to rest on the ground, were contioued as high as the mist, and in breadth near half as much more as that of the iris. In the middle, between these two places, on the same horizontal line, was a coloured appearance like dcb, a, bcd, whose base could not at most subtend an angle of above ten or twelve degrees, and whose interior parts were thus variegated. The centre a was dark and irregularly terminated, as if made by the shadow of some object not larger than an ordinary sheal of corn. Next this centre was a curved space bb, of a yellowish flame.colour. To this succeeded another curved space of nearly the same dark cast as the centre, seemingly tinged with a faint blue green, and very evenly bounded on each side, as at cc. After these came on the terminating ring, which was coloured very much in the manner of the common rainbow, except that the tints were not quite so vivid (as if owing to the effect of a yellowish tinge, which seemingly entered into the composition of all the colours) nor their boundaries so well defined. The centre of the image appeared to be exactly in the line of aspect, as it is called, or one conceived to be drawn from the sun through the eye of the spectator: and it may be observed from the figure, that these curve spaces were not segments of perfect circles, but formed like the ends of concentric ellipses, whose transverse axes were perpendicular to the horizon.
To the above description of the image it may be necessary to add the following particulars which attended it. The mist was very thick near the surface of the meadows, though rarer upwards, and chiefly, if not solely, on the side of the hill opposite to the sun. T'he place where Mr.C. stood was just on its confines; and as he advanced into it, the object became gradually fainter and fainter. As the sun dispersed the vapour, the appearance faded propor. tionably; and about half an hour after he first saw it, it was scarcely visible. The evening before was wet; but the drops on the hedges were congealed by frost. Where the sun shone, the bushes were each invested with a mist, as if owing to the vapours exhaled from them by the sun's warmth ; and, on a nearer inspec. tion, he could clearly discern the little humid particles which occa. sioned it, and which were floating around the bushes at about half an inch distance from each other.
Peculiar solar and lunar Irises seen in South America.
To the before mentioned particulars of the mountainous deserts, I shall subjoin the phænomena seen there, as subjects equally meriting the curiosity of a rational reader. At first we were greatly surprised with two, on account of their novelty ; but frequent observations rendered them familiar. One we saw in Pambamarca, on our first ascent thither; it was a triple circular iris. At break of day the whole mountain was encompassed with very thick clouds, which the rising of the sun dispersed so far as to leave only some vapours of a tenuity not cognizable by the sight: on the opposite side to that where the sun rose, and about ten toises distant from the place where we were standing, we saw, as in a looking-glass, the image of each of us, the head being as it were the centre of the three con. centric irises : the last or most external colours of one touched the first of the following ; and at some distance from them all, was a fourth arch entirely white. These were perpendicular to the ho. rizon ; and as the person moved, the phenomenon moved also in the same disposition and order. But what was most remarkable, though we were six or seven together, every one saw the phenome. non with regard to himself, and not that relating to others. The diameter of the arches gradually altered with the ascent of the son above the horizon; and the phenomenon itself, after continuing a long time, insensibly vanished. In the beginning, the diameter of