Astronomy: an atmospheric condition producing sun dogs, giving the effect of two suns. Engraving by F.R. Hay, 1820, after W.M. (?) Craig.

Astronomy: an atmospheric condition producing sun dogs, giving the effect of two suns. Engraving by A. Hay, 1820, after H.D. Craig.

An episode observed by William Whiston on 22-23 October 1721 at Lyndon, County of Rutland, and published in the Philosophical transactions of the Royal Society in 1721. Whiston is presumably the man on the left of the print, observing the phenomenon. He resided at Lyndon Hall which was the family home of his son-in-law Samuel Barker

"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 towards 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 inverted bright arc, though its bend as 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 23; semidiameter of the arc of the rainbow, if our vertex be supposed its centre, 21°. The phenomenon lasted each day for an hour and a half, or two hours . …"-Whiston, in Polehampton and Good, loc. cit.

London (46 Holborn Hill) : R. N. Rose, May 1 1820.

1 print : engraving, with etching

Two mock suns. Engraved by Hay from a drawing by Craig for the Gallery of nature and art.

"From a drawing by Craig": most likely to be understood as referring to the prolific illustrator William Marshall Craig (ca. 1764-1829), but there was also an H.D. Craig who exhibited at the Royal Academy in 1815 and 1817

William Whiston, 'Two mock-suns , and an arc of a rainbow inverted , with a halo', Philosophical transactions of the Royal Society, 31 December 1721, vol. 31, pp. 212-215.

Wellcome Collection 46620i