which proceed I from the Sun. 313 



whose diameters would subtend an angle more than ten 

 times sweater than this separation of their centres, would 

 appear~in the heavens not entirely to coincide, but to over- 

 lap one another, as represented in fig. I. (Plate IX.) where 

 the strong marked circle stands for the sun's usual white 

 disk, and the faint one for the disk corresponding to the 

 supposititious violet rays, and the line EC for the ecliptic 

 passing through the centres of both. 



The consequence of this overlapping would be remark- 

 able. We should behold what now might be called a com- 

 pound disk of the sun, a little drawn out or elongated in 

 the direction of the ecliptic, and having the lunula or cres- 

 cent W shining with white light, forming its eastern limit, 

 and an equal and opposite c/escent V shining with the 

 supposititious violet light, while the intermediate portion of 

 the disk bounded by the two crescents GGGG, would shine 

 \vij:h both the white and violet light blended together, 



The very same description would equally apply to an image 

 of this kind of sun, formed by a large object-glass of long 

 focal distance, on a white screen or plane placed at the focus, 

 and perpendicular to the principal axis of the lens. The 

 image formed on the screen would consist of the white and 

 violet crescents, and the intermediate space of a mixed co- 

 lour ; only inverted as in fig. 2 ; just as it would be were 

 there no aberration in the case, and as if such a party-co- 

 loured sun as in fig. 1, really shone in the heavens, the 

 earth being supposed at rest. 



To draw nearer to what is ultimately to be illustrated by 

 this detail, let it next be supposed, that either the calorific 

 or the deoxidizing rays were emitted by the sun, in place of 

 the violet rays above mentioned, with the same slow velo- 

 city, but agreeing with the sun's white light in refrangi- 

 bilitv. Then it is evident that the rays of caloric, for in- 

 stance, would be collected in the very same circular space 

 on the screen which was formerly occupied by the violet 

 rays ; that is, within the space defined by the Joint circle, 

 fig. 2. The consequence of this would be, that the portion 

 of the bright image represented by the crescent W would 

 he wholly ^deprived of the rays of caloric, whilst the rest 

 of the image would be overspread by such rays. Further, 

 Jt is manifest that another space V beyond the image, but 

 bounding it, corresponding to the former violet crescent, 

 would also be overspread by the rays of caloric. 



Thus, therefore, would the sun's bright image on the 

 Screen be attended with extraordinary circumstances, which, 

 though not in the least perceivable in. the first instance by 



Y 3 our 



