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.

The reason why Goethe chose optics as the field of conflict, and devoted to it more than twenty years of research and reflexion, amidst all the other labours of his rich life, lay certainly in his individual temperament - 'zum Sehen geboren, zum Schauen bestellt'.¹ At the same time one must see here a definite guidance of humanity. Since the hour had struck for mankind to take the first step towards overcoming the world-conception of the one-eyed, colour-blind onlooker, what step could have been more appropriate than this of Goethe's, when he raised the eye's capacity for seeing colours to the rank of an instrument of scientific cognition?

Goethe describes in this book the basic phenomena of the creation of the prismatic colours, with particulars of a number of experiments so arranged that the truth he had discovered, contrary to Newton's view, comes to light through the very phenomena themselves. Only much later, in the year 1810, and after he had brought to a certain conclusion four years previously the researches which he had pursued most carefully the whole time, did he make public the actual masterpiece, Entwurf einer Farbenlehre.⁷ (An English translation of the didactic part appeared about ten years after Goethe's death.)

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.

In point of fact, the essential difference between Goethe's theory of colour and the theory which has prevailed in science (despite all modifications) since Newton's day, lies in this: While the theory of Newton and his successors was based on excluding the colour-seeing faculty of the eye, Goethe founded his theory on the eye's experience of colour.

While leaving a more detailed description of the composition of Goethe's Entwurf for our next chapter, we shall here deal at once with some of the essential conclusions to which the reader is led in this book. As already mentioned, Goethe's first inspection of the colour-phenomenon produced by the prism had shown him that the phenomenon depended on the presence of a boundary between light and darkness. Newton's attempt to explain the spectrum out of light alone appeared to him, therefore, as an inadmissible setting aside of one of the two necessary conditions. Colours, so Goethe gleaned directly from the prismatic phenomenon, are caused by both light and its counterpart, darkness. Hence, to arrive at an idea of the nature of colour, which was in accord with its actual appearance, he saw himself committed to an investigation of the extent to which the qualitative differences in our experience of colours rests upon their differing proportions of light and darkness.

If one exposes an arrangement like this to the action of the prism, whose position has remained unchanged, colours appear on each of the two edges, as before, but in reverse order (Fig. iii). The spectral phenomenon now begins at one side with light blue and passes into indigo and violet, with uncoloured darkness in the centre. From this darkness it emerges through red and passes through orange to yellow at the other end.

In view of the present scientific conception of the effect which a prismatic piece of a transparent medium has on light passing through it, Goethe's objection to Newton's interpretation and the conclusions drawn from it seems by no means as heretical as it did in Goethe's own time and for a hundred years afterwards. For, as Lord Rayleigh and others have shown, the facts responsible for the coming into being of the spectral colours, when these are produced by a diffraction grating, invalidate Newton's idea that the optical apparatus serves to reveal colours which are inherent in the original light. Today it is known that these colours are an outcome of the interference of the apparatus (whether prism or grating) with the light. Thus we find Professor R. W. Wood, in the opening chapter of his Physical Optics, after having described the historical significance of Newton's conception of the relation between light and colour, saying: 'Curiously enough, this discovery, which we are taking as marking the beginning of a definite knowledge about light, is one which we shall demolish in the last chapter of this book,² for our present ideas regarding the action of the prism more nearly resemble the idea held previous to Newton's classical experiments. We now believe that the prism actually manufactures the coloured light.'

It is characteristic of Goethe's whole mode of procedure that he at once changed the question, 'What is colour?' into the question, 'How does colour arise?' It was equally characteristic that he did not, as Newton did, shut himself into a darkened room, so as to get hold of the colour-phenomenon by means of an artificially set-up apparatus. Instead, he turned first of all to nature, to let her give him the answer to the questions she had raised.

Again, where the two interior colour-cones merge, there an additional colour appears. Like green, it is of a neutral character, but at the same time its quality is opposite to that of green. In Newtonian optics, which assumes colour to be derived from light only, this colour has naturally no existence. Yet in an optics which has learnt to reckon with both darkness and light as generators of colour, the complete spectrum phenomenon includes this colour equally with green. For lack of an existing proper name for it, Goethe termed it 'pure red' (since it was free from both the blue tinge of the mauve, and the yellow tinge of the red end of the ordinary spectrum), or 'peach-blossom' (pfirsichblüt), or 'purple' (as being nearest to the dye-stuff so called by the ancients after the mollusc from which it was obtained).¹⁰