• of Vision described by Mr. Smith of Fochabers. 171 



bright green, (though the light passed only through the eye- 

 lid,) and fully as green as it* the eye had been open; — and 

 what is interesting, the other white slip instantly becomes 

 reddish, which now can only happen from contrast. 



I have mentioned in a former paper (vol. i. p. 172.), that 

 a stick of red sealing-wax seen by a highly-excited part of 

 the excited eye w r as of a dark liver colour ; while to the other 

 eye its colour was brilliantly red. By substituting the follow- 

 ing coloured fluids in place of the slip of paper, and illumi- 

 nating them by transmitted light, I observed them to change 

 their tints, as shown in the following table. — The experiments 

 were made in candle-light. 



Colour to the Colour to the 



Colour. excited Eye. uncxcited Eye. 



Nitrate of copper* . . Greenish blue. Deep blue. Pale bluish white. 



Carbazotic acidf Yellow. Green yellow. Orange yellow. 



iron " ana G ° I O ran § e red. Yellowish red. More orange red. 

 Meconate of iron . . . Ditto. Ditto. Ditto. 



Oxalate of chro- ] n . j rv i i r> j 



- _ i .i r Port- wine red. Pink red. Red. 



mium and potash J 



Bichromate of pot-i 



ash and arsenious > Green. Bright green. Yellowish green. 



acid J 



Chloride of cobalt . . . Pale red. Paler red. Brighter red. 



A " er° n . i . Ure !. 0f °T. } Blue ' Indi S°- B,ue ' 



Nitrate of nickel .... Green. Bright green. Yellowish green. 



Muriate of copper . . Whitish green. Bright green. Whitish yellow. 



Purple glass Purple. Pink red. Brick red. 



Green glass Green. Bright green. Yellowish green. 



In all these experiments, where the effect is well marked, the 

 image in the unexcited eye receives as it were an addition of 

 the less refrangible rays, while the other image loses a portion 

 of the same rays, — results which are entirely accordant with 

 our previous observations. 



Mr. Smith next proceeds to a very delicate and somewhat 

 speculative task, into which we are not much disposed to fol- 

 low him ; namely, to ascertain the causes which excite the eye 

 to see the slip of paper green and red, and the purposes for 

 which these causes are called into action. He conceives the 

 exciting causes to be the indistinct vision, and the heteroge- 

 neous or white colour of the exciting light; that is, if the ex- 

 citing light is homogeneous, and seen distinctly, the comple- 

 mentary red and green colours are no longer visible. 



Mr. Smith's experiment, No. 8, p. 344*, is destined to prove 

 that when the exciting light is seen distinctly, the images of 



* This solution gave a spectrum in^which there were no red or orange rays, 

 f No blue in its spectrum. 



Z2 



