468 POPULAR SCIENCE MONTHLY. 



refrangibility, they by their unequal refractions must be severed and 

 dispersed into an oblong form in an orderly succession, from the least 

 refracted scarlet, to the most refracted violet. And for the same 

 reason it is that objects, when looked upon through a prism, appear 

 coloured. For the difform rays, by their unequal refractions, are 

 made to diverge towards several parts of the retina, and there express 

 the images of things coloured, as in the former case they did the sun's 

 image upon a wall. And by this inequality of refractions they become 

 not only coloured, but also very confused and indistinct. 



10. Why the colours of the rainbow appear in falling drops of 

 rain, is also from hence evident. For, those drops which refract the 

 rays disposed to appear purple, in greatest quantity to the spectator's 

 eye, refract the rays of other sorts so much less, as to make them pass 

 beside it; and such are the drops on the inside of the primary bow, 

 and on the outside of the secondary or exterior one. So those drops, 

 which refract in greatest plenty the rays apt to appear red, towards 

 the spectator's eye, refract those of other sorts so much more, as to 

 make them pass beside it; and such are the drops on the exterior part 

 of the primary, and interior part of the secondary bow. 



11. The odd phenomena of an infusion of lignum nephriticum, 

 leaf gold, fragments of coloured glass, and some other transparently 

 coloured bodies, appearing in one position of one colour, and of 

 another in another, are on these grounds no longer riddles. For, 

 those are substances apt to reflect one sort of light, and transmit 

 another; as may be seen in a dark room, by illuminating them with 

 similar or uncompounded light. For, then they appear of that colour 

 only, with which they are illuminated, but yet in one position more 

 vivid and luminous than in another, accordingly as they are disposed 

 more or less to reflect or transmit the incident colour. 



12. From hence also is manifest the reason of an unexpected experi- 

 ment, which Mr. Hook, somewhere in his micrography, relates to 

 have made with two wedge-like transparent vessels, filled the one 

 with red, the other with a blue liquor: namely, that though they were 

 severally transparent enough, yet both together became opaque; for, 

 if one transmitted only red, and the other only blue, no rays could 

 pass through both. 



13. I might add more instances of this nature; but I shall con- 

 clude with this general one, that the colours of all natural bodies have 

 no other origin than this, that they are variously qualified to reflect 

 one sort of light in greater plenty than another. And this I have 

 experimented in a dark room, by illuminating those bodies with un- 

 compounded light of divers colours. For, by that means, any body 

 may be made to appear of any colour. They have there no appropriate 

 colour, but ever appear of the colour of the light cast upon them, 



