ON CHANGEABLE COLOURS. 130 



«?qua], except the concentrated muriatic acid, which showed 



some diflference; and all their effects ceased nearly alike on and disappear- 

 - , ed on drying, 



arymo^. 



When the exterior orbit of the eye was wetted, its yellow- The colours 

 ish colour became of a lively blood red; and the reflection, thus produced, 

 which was before p^reen when seen obliquely, was almost de- 

 stroyed. If the green space within were wetted, it was the 

 violet reflection that disappeared. Lastly with smoking mu- 

 riatic acid this green space viewed perpendicularly exhibited 

 a yellow inclining strongly to red, and the oblique reflection 

 changed at first to green, and then it passed on to violets 

 none of these changes however continued permanent. 



By wetting in this manner the extremity of the feathers Feathers of a 

 of a turkey's tail, I brought out very vivid new colours, ^^ ^^ ^ 

 which could not be perceived before in the same direction ; 

 Jbut the existence of which was indicated by certain reflec- 

 tions when viewed with the back to the light, analogous to 

 those I mentioned in speaking of the duck's feathers. 



It was impossible for me, after all these particularities, to Perhaps from 



persist in classing together the changing colours of feathers, ^^'^^ ^'^y^!'^°^^' 

 W' A,u ^.U 1 J • c u- ^ A r. 'rionofdiffer- 



c; una those ot the coloured nngs ot pellicles. An otten re- ent coloured 



peated examination of them at length suggested the idea, substances. 

 that they might arise from the superposition of different co- 

 loured substances, sometimes of two only, or of three, or of 

 a greater number ; nearly as if, wishing to paint a body with 

 several colours, we were to cover it in succession with a stra- 

 tum of each of the proposed ingredients. 



. This supposition, suitably adapted to each part of the This Hlustrat- 

 feathers, very well accounts for all the appearances observed. ^^• 

 In fact, if over a coat of green paint for instance we spread 

 a thin stratum of a violet powder, it is obvious, that on look- 

 ing directly at it it will appear almost wholly green; while 

 on lowering the eye, so as to view it obliquely, the violet 

 will gradually predominate, till at length it alone is seen. 

 The intermediate tiuts will be different shades of green, to 

 which various shades of blue will succeed, before the violet 

 will appear. 



' If in addition to this the green itself be laid on a red 

 i ground, this may remain invisible in the intervals of the co* 

 , loured matter of the superior strata : but if these strata be 



rendered 



