Faithful to his question, ‘How does colour arise?’ Goethe now proceeded to investigate under what conditions two borders, when placed opposite each other, provide a continuous band of colour – that is, a colour-band where, in place of the region of uncoloured light, green appears. This, he observed, came about if one brought one’s eye, or the screen intercepting the light, to that distance from the prism where the steadily widening yellow-red and the blue-violet colour-cones merge (Fig. ii).⁹ Obviously, this distance can be altered by altering the distance between the two borders. In the case of an extremely narrow light-space, the blue and yellow edges will immediately overlap. Yet the emergence of the green colour will always be due to a union of the blue and yellow colours which spread from the two edges. This convinced Goethe that it is inadmissible to place the green in the spectrum in line with the other colours, as is customary in the explanation of the spectrum since Newton’s time.