624 PHILOSOPHICAL TRANSACTIONS. [aNNO 1723. 



that we could not steadily tix our eyes upon it. Thus the order of the colours 

 was, 1. Red, orange colour, yellow, green, light blue, deep blue, purple. 

 2. Light green, dark green, purple. 3. Green, purple. 4. Green, faint 

 vanishing purple. 



There are two things which well deserve to be taken notice of, as they may 

 perhaps direct us in some measure to the solution of this curious phenomenon. 

 The 1 St is, that the breadth of the first series so far exceeded that of any of 

 the rest, that it was equal to them all taken together. The 2d is, that I have 

 never observed these inner orders of colours in the lower parts of the rainbow, 

 though they have often been incomparably more vivid than the upper parts, 

 under which the colours have appeared. I have taken notice of this so very 

 often, that I can hardly look upon it to be accidental; and if it should prove 

 true in general, it will bring the disquisition into a narrow compass ; for it will 

 shew that this effect depends on some property which the drops retain while 

 they are in the upper part of the air, but lose as they come lower, and are more 

 mixed with each other. 



On the ahovementioned Appearance in the Rainbow, with some other Reflections 

 on the same Subject. By Henry Pemberton, M.D. R. S. S. N° 375, p. 245. 



Let AB, fig. 1, pi. l6, represent a drop of rain, b the point from whence 

 the rays of any determinate species being reflected to c, and afterwards emerg- 

 ing in the line cd, proceed to the eye, and cause the appearance of that colour 

 in the rainbow, which appertains to this species. It is observed by Sir Isaac 

 Newton, Optics, book 2, part 4, that in the reflection of light, besides what 

 is reflected regularly, some small part of it is irregularly scattered every way. 

 So that from the point b, besides the rays that are regularly reflected from b to 

 c, some scattered rays will return in other lines, as in be, bf, bg, bh, on each 

 side the line bc. Further, it must be noted from Newton, Optics, part 2, 

 prop. 12, that the rays of light, in their passage from one superficies of a 

 refracting medium to the other, undergo alternate fits of easy transmission and 

 reflection, succeeding each other at equal intervals; insomuch that if they 

 reach the farther superficies in one sort of those fits, they shall be trans- 

 mitted; if in the other kind of them, they shall rather be reflected back. 

 Whence the rays that proceed from b to c, and emerge in the line cd, being 

 in a fit of easy transmission, the scattered rays that fall at a small distance 

 without these on either side, suppose the rays, that pass in the lines be, bg, 

 shall fall on the surface in a fit of easy reflection, and shall not emerge; but 

 the scattered rays that pass at some distance without these last, shall arrive at 

 the surface of the drop in a fit of easy transmission, and break through that 



