VOL. XXXI.] PHILOSOPHICAL TRANSACTIONS. 533 



w. s. w. I saw an attempt towards two mock-suns, as I had done sometimes 

 formerly. About 4- or -|- 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, fig. 16, pi. 14, 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 10 

 or 12 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 conimon 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 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 224-° J perpendicular semidiameter of the halo 234.° ; 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. What was most remarkable on 

 Monday was, that the wind, which on Sunday had been almost insensible, was 

 now become sensible, and changed to n.n.k. that the halo was sensibly be- 

 come 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 horizontal 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 Q 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 no- 

 Transactions. A few years before his deaths he published Memoirs of his own life and writings, 

 which are very curious. 



