tOLORIFlCATlON IN GENERAL. 331 



agency of pure and colorless light, never had 

 an existence on the skin, but that they are 

 repelled and excluded from it; and that 

 it is polluted and defaced by the rays alone 

 which are absorbed within, and not reflected 

 without, viz. the orange, the yellow, the green, 

 the violet, the indigo, the purple, the black. 



So far, however, from subscribing to these 

 opinions, however great the authority may be 

 from whence they are derived, [ feel it my duty 

 to protest against them, and endeavour to ex- 

 pose the absurdities to which they lead : they 

 have, I conceive, been occasioned by an igno- 

 rance of physiology, by not knowing the rela- 

 tion which exists between the sensitive prin- 

 ciple within, and the substance without, by 

 which sensation is excited and produced. In- 

 stead of ascribing sensation to the receiver, it 

 has rather been referred to the thing received, 

 and impression and sensation have thereby been 

 confounded together. 



Instead of supposing that the pure solar rays 

 (which in their simple and uncombined state, I 

 have endeavoured to shew are colorless and in- 

 visible) are colored originally and essentially ; 

 or, that the infinite variety of colors which AVC 

 behold, are formed out of the prismatic alone, 

 I conceive it far more reasonable to conclude, 

 that the pure solar rays are the carriers and the 

 agents only ^ that not only the formation, but 



