INTRODUCTION. 
When I first proposed to publish on Colours, it was merely with 
an intent of simplifying the means of mixing them, and that chiefly 
with regard to such as are used for painting in water or oil, with a 
particular desire to show a means of agreement and ready reference 
among naturalists and others, as to their identity. This led me to 
inquire for some permanent and constant means of comparison, from 
some original source that might always be consulted, and leave no 
room for doubt. Observing a sort of originality in the prismatic 
tints of stones, and that I could trace their order, I began with 
them ; but, after all, finding them too fixed as it were for some 
purposes, and that it would be desirable to mix or unmix the 
original prismatic tints with the same order as common colours, and 
perceiving a strange want of agreement in this particular among 
philosophers, &c., I was the more anxious, especially as to the ob- 
taining the same three primitives as were pretty universally allowed 
to common colours, viz. Yellow, Red and Blue ; for should Nature 
agree in this, which seemed to me a desideratum, I might then find 
a means of producing them so as to mix them perfectly, and be able 
to come to some fair conclusion. I made a few inquiries upon the 
subject, but to no purpose, as it was generally thought impossible: 
and having a further desire to measure them, it seemed to be consi- 
dered as a vanity. I was however satisfied, that as there was some- 
thing wanted to make the desired agreement, so it might possibly 
B 
