For when three are combined, the colours are debased; and 
when mixed in a certain proportion, destroyed;* and black, or 
darkness, the privation of light or colour produced. Without 
entering at all into the question before alluded to, respecting the 
prismatic colours, it is certain from experience, that even with 
our gross materials, we can produce, by different mixtures of the 
three prismatic colours, Yellow, Red, and Blue, colours similar to 
all the other etherial prismatic tints, although in a degree very 
far inferior in point of beauty. We see them arrayed by nature 
in harmonious succession; and if we interrupt that succession, we 
perceive the harmony is immediately destroyed; for the three 
primitive colours being, as before observed, of different natures, 
they will not associate together; but require the mediation of 
a third colour, formed by a mixture of any two of these three 
colours. It is that mixture, then, tvhich produces the harmony so 
pleasing to the eye, and which conducts it insensibly from one 
to another; we will say from Yellow io Green, and from Green to 
Blue ; or in like manner, from Yellow to Orange, from Orange 
to Red, from Red to Violet, and from Violet to Blue. Thus the 
eye travels gradually from one to another of the three primitive 
colours, without being offended by too quick a transition from one to 
* For that proportion which produces black See page 12. 
