Abstract
THE accompanying drawing—a copy of a sketch taken at the time—represents an unusual atmospheric phenomenon witnessed by several friends and myself during a recent visit to Ireland. It occurred on the 6th inst., a bright warm day, with a light breeze blowing from the east. The sky was free from clouds, excepting a few cirrus and cirro-stratus collections on the northern horizon. Engaged at the time in fishing from a boat on one of the Irish loughs, I was conscious of a change in the character of the light reflected from the water and distant objects and looking towards the sun (f), noticed that it was surrounded by an exceedingly brilliant halo (a b) of about 48° diameter, the contained space (g h) being filled with vapour of a dull leaden blue colour, which, by obscuring some of the solar rays, apparently produced the peculiar light effects that first attracted my attention. The time was 1.30 in the afternoon. Calling the attention of my friend, Dr. Simpson, to the phenomenon, I recorded the accompanying details. The primary liula (a b) consisted of a brilliant, well-defined band of about 8 width, composed of the spectral colours in the usual sequence, the red ring being nearest the sun. The whole band was most vivid, but the northern half the brightest. At about two o'clock I noticed a bulging (i) of the leaden-coloured vapour of the primary halo (a b) to the extent of 6° or 7°, and in its south-eastern quadrant, and this protrusion, at first only faintly fringed with colour, soon was bounded by a spectral bow (e) at least as vivid as the brightest portion of the primary halo. The adjacent portion of a b, whether by comparison with e or whether because partially obscured by the protrusion of the vapour around which e was formed, I cannot be sure, seemed much paler than the rest of a b. Simultaneously with the formation of this secondary bow a large white ring, represented in the drawing by c d, slowly formed around a centre to the north of the sun, and rapidly assumed a well-defined contour. Its diameter was 72°. Had it been complete it would in its southern portion have passed through the sun, but after cutting the primary halo (a b) at the points (m and n), which it rendered more faint, it gradually disappeared before reaching the sun. This latter ring (c d) began to disappear about a quarter of an hour after I first noticed it, its north western portion fading first. I noticed no mock-suns at the points of contact of either of the excentric rings, and was, unfortunately, unprovided with my small pocket polariscope, and therefore unable to ascertain how much of the phenomenon was due to double refraction. The portion (e) may have been thus produced, but it certainly appeared, as drawn, to be a portion of a ring of smaller radius than (a b). The Rev. T. G. Beaumont, who also observed this spectacle, states that he saw the primary halo (a b) gradually start from a much smaller ring around the sun. The accompanying drawing, though rough, is as accurate as compatible with the absence of measuring instruments.
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HODGKINSON, A. Unusual Atmospheric Phenomenon. Nature 32, 173 (1885). https://doi.org/10.1038/032173b0
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DOI: https://doi.org/10.1038/032173b0
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