798 PROFESSOR PIAZZI SMYTH ON COLOUR, 
now proceed to examine the received Jaws touching the colour-blind : chiefly as 
they have been well and succinctly collected by Professor EVERETT, in that use 
ful book of reference, his edition of DESCHANEL’s Natural Philosophy. 
The chief, of these long since postulated maxims,—(but wherein I am sorry 
to say, though colours are abundantly dealt with, the difference of physical con- 
stitution among matters held as showing to the eye one and the same colour,— 
is not at all, or barely, touched on)—are as follows,— 
(1) “What is called colour-blindness has been found, in every case which 
has been carefully investigated, to consist in the absence of the elementary 
sensation corresponding to red. 
(2) “The scarlet of the spectrum is thus visible to the colour-blind, not as 
scarlet, but as a deep, dark colour, probably a kind of dark green. 
(3) “To such an eye, any colour can be matched by a mixture of yellow and 
blue, and such vision may therefore be called di-chroic.* 
(4) ‘Objects which have the same colour to a tri-chroic (an ordinary) eye, 
have also the same colour to a di-chroic (colour-blind) eye.” 
To those most clearly stated laws, the following practical answers may now 
be rendered, as I am led to believe by the di-chroic medium, on the part of at 
least a large section of the colour-blind :— 
(1’). In the case most characteristic of orthodox colour-blindness, viz., con- 
fusing between bright red and bright green,—it is not as laid down that the 
red is not seen, but that the green appears also as red ; in fact just as red as 
the red. 
(2’). As for the scarlet of the spectrum being said to be seen by such of the 
colour-blind only as a dark green or other dull colour,—it is seen by them more 
purely, gloriously, entirely red than by any other class of persons. 
(3’). To say, that to any one with a colour-blind eye, which really sees red 
so grandly, as those looking through a strongly di-chroic fluid must do,—to say, 
I repeat, that any colour can be matched by a mixture of yellow and blue,—is 
simply a mistake. And such mistake has originated probably from some of the 
yellows shown to the parties concerned, being those which, to them, appeared 
more or less red. Thus IJ, looking through the colour-blinding, or rather di- 
chroicising medium, see in my colour box 
Lemon yellow=faint rose pink set off in places with pale French gray. 
Naples yellow=orange red-lead. Cadmium yellow=vermilion red-lead. While 
Gilding, reminds me of the “red-gold” of rustic fairy-tales and song. 
(4’). Objects which have the same colour to a tri-chroic, have the same to a 
di-chroic, eye,—says the law. Wherefore I look with my natural tri-chroic eye 
at Venetian green blinds, and at green grass, and see the two objects of the 
* Readers will please to note the different meaning here attached to this word, as compared to 
that in which we have ourselves been employing it spectrally, and must employ it again. 

