Colour of Small Objects

Abstract

IF a circle, 2 cm. in diameter, is divided into quadrants and coloured as in Fig. 1, placed on either a black or white ground, and then viewed with one eye from a distance of about 3 m., it will be found that there is considerable difficulty in distinguishing the green from the light blue on one hand and the orange-brown from the light red-purple on the other, so long as the brightnesses of the fields are made as equal as possible. There will be no difficulty in distinguishing the green from the orange, provided that the observer is not red-green colour-blind in the sense that he habitually confuses such colours, and the circle will appear to be divided into two halves, right and left. Red-green colour-blind observers see the circle as uniform, or they may be able to separate the quadrants on subtle brightness differences.