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. This insight into the relation of the central colour of the continuous spectrum to its other colours still further strengthened Goethe's conviction that in the way man experiences nature in his soul, objective laws of nature come to expression. For just as we experience the colours on the blue side of the spectrum as cold colours, and those on the yellow side as warm colours, so does green give man the impression of a neutral colour, influencing us in neither direction. And just as the experience of the two polar colour-ranges is an expression of the objective natural law behind them, so too is the experience of green, the objective conditions of whose origin give it a neutral position between the two. With this it also became clear why the vegetative part of the plant organism, the region of leaf and stem formation, where the light of the sun enters into a living union with the density of earthly substance, must appear in a garment of green. * Having in this way found the clue to the true genesis of the spectrum, Goethe could not fail to notice that it called for another - a 'negative' spectrum, its polar opposite - to make the half into a whole. For he who has once learnt that light and darkness are two equally essential factors in the birth of colour, and that the opposing of two borders of darkness so as to enclose a light is a 'derived' (abgeleitet) experimental arrangement, is naturally free to alter the arrangement and to supplement it by reversing the order of the two borders, thus letting two lights enclose a darkness between them.