AS PERCEIVED BY THE EYE. 293 
increased, the disc appears perfectly uniform in colour. From these experiments 
it appears, that the apparent mixture of colours is not due to a mechanical super- 
position of vibrations, or to any mutual action of the mixed rays, but to some 
cause residing in the constitution of the apparatus of vision. 
(7.) Presentation of the Colours to be mixed one to each Eye. 
This method is said not to succeed with some people; but I have always 
found that the mixture of colours was perfect, although it was difficult to con- 
ceive the oljects seen by the two eyes as identical. In using the spectacles, of 
which one eye is green and the other red, I have found, when looking at an ar- 
rangement of green and red papers, that some looked metallic and others trans- 
parent. This arises from the very different relations of brightness of the two 
colours as seen by each eye through the spectacles, which suggests the false con- 
clusion, that these differences are the result of reflection from a polished surface, 
or of light transmitted through a clear one. 
Notts II. 
Results of Experiments with Mr Hay’s Papers, at Cambridge, November 1854. 
The mean of ten observations made by six observers gave— 
| 449 R+-299 G+-252B=-224W+776Bk  . «wD. 
696 R+:304 G=:181 B+°327 Y +:492 Bk H : : “ehh CDH 
These two equations served to determine the positions of white and yellow in 
{ diagram No. 2. The coefficient of W is 4-447, and that of yellow 2:506. 
From these data we may deduce three other equations, either by calculation, 
_ or by measurement on the diagram (No. 2). 
Eliminating green from the equations, we find— 
+565 B+ -485 Y=-307 R+-304 W+°389 Bk ; F ; Sh); 
_____ The mean of three observations by three different observers, gives— 
E 573 B+°:477 Y='313 R+-297 W +:390 Bk 
_ Errors of calculation, —-008 B+-008 Y—-006 R+:007 W—-001 Bk 
‘ The point on the diagram to which this equation corresponds is the intersection 
of the lines BY and RW, and the resultant tint is a pinkish-gray. 
q Eliminating red from the equations, we obtain— 
Calculation, . 533 B+:150 G@+-317 Y=:337 W+:663 Bk 
_ By 10 observations, -537 B++146 G+-317 Y=-337 W +663 Bk 
Bw (a)s 
Errors, . - —004 +-004 — — — 
Eliminating blue, 660 R+-340 G=:218 Y+-108 W+-682 Bk 
By 5 observations, -672 R+-328 G=:224 Y+:094 W+-672 Bk : : soe {@)) 
Errors, . - —012 +:012 —-006 +014 +008 f 
