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For this purpose he borrowed a set of prisms from a friend living in near-by Jena, the physicist, Büttner. Since, however, he had at that time no opportunity of arranging a dark chamber on Newton’s lines, where the necessary ray of light from a tiny hole in the window-covering was sent through a prism, he postponed the whole thing, until in the midst of all his many other interests and duties it was forgotten. In vain Büttner pressed many times for the return of the prisms; at last he sent a mutual acquaintance with the injunction not to return without them. Goethe then searched for the long-neglected apparatus and determined to take a rapid glance through one of the prisms before he gave them back.

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There seems to be no suitable word in English for rendering the term trübe in the sense in which Goethe used it to denote the optical resistance of a more or less transparent medium. The following remarks of Goethe’s, reported by his secretary Riemer, will give the reader a picture of what Goethe meant by this term, clear enough to allow us to use the German word. Goethe’s explanation certainly shows how inadequate it is to translate trübe by ‘cloudy’ or ‘semi-opaque’ as commentators have done. ‘Light and Dark have a common field, a space, a vacuum in which they are seen to appear. This space is the realm of the transparent. Just as the different colours are related to Light and Dark as their creative causes, so is their corporeal part, their medium, Trübe, related to the transparent. The first diminution of the transparent, i.e. the first slightest filling of space, the first disposition, as it were, to the corporeal, i.e. the non-transparent – this is Trübe.‘⁸

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Moreover, as Eddington shows, the question whether the optical contrivance ‘sorts out’ from the chaotic light a particular periodicity, or whether it ‘impresses’ this on the light, becomes just ‘a matter of expression’.¹¹ So here, too, the modern investigator is driven to a resigned acknowledgment of the principle of Indeterminacy.

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He recalled dimly his pleasure as a boy at the vision of the world given him through a bit of similarly shaped glass. ‘I well remember that everything looked coloured, but in what manner I could no longer recollect. I was just then in a room completely white; remembering the Newtonian theory, I expected, as I put the prism to my eye, to find the whole white wall coloured in different hues and to see the light reflected thence into the eye, split into as many coloured lights.

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After Goethe had once determined from the macrotelluric phenomenon that an interplay of light and darkness within Trübe was necessary for the appearance of colour in space, he had no doubt that the prismatic colours, too, could be understood only through the coming together of all these three elements. It was now his task to examine in what way the prism, by its being trübe, brings light and darkness, or, as he also expressed it, light and shadow, into interplay, when they meet at a boundary.

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No such conclusions are forced upon the one who studies the spectrum phenomenon with the eyes of Goethe. Like the modern experimenter, he, too, is faced with the question ‘Discovery or Manufacture?’ and he, too, finds the answer to be ‘Manufacture’. But to him nature can disclose herself as the real manufacturer, showing him how she goes to work in bringing about the colours, because in following Goethe he is careful to arrange his observations in such a way that they do not veil nature’s deeds.

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‘But how astonished was I when the white wall seen through the prism remained white after as before. Only where something dark came against it a more or less decided colour was shown, and at last the window-bars appeared most vividly coloured, while on the light-grey sky outside no trace of colouring was to be seen. It did not need any long consideration for me to recognize that a boundary or edge is necessary to call forth the colours, and I immediately said aloud, as though by instinct, that the Newtonian doctrine is false.’

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We must remember that on first looking through the prism Goethe had immediately recognized that the appearance of colour is always dependent on the existence of a boundary between light and darkness – in other words, that it is a border phenomenon. What colours appear on such a border depends on the position of light and darkness in relation to the base of the prism. If the lighter part is nearer to the base, then blue and violet tints are seen at the border, and with the reverse position tints of yellow and red (Plate B, Fig. i). Along this path of study Goethe found no reason for regarding the spectrum-phenomenon as complete only when both kinds of border-phenomena appear simultaneously (let alone when – as a result of the smallness of the aperture through which the light meets the prism – the two edges lie so close that a continuous band of colour arises). Hence we find Goethe – unlike Newton – treating the two ends of the spectrum as two separate phenomena.

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‘As for what I have done as a poet, I take no pride in it whatever. Excellent poets have lived at the same time as myself; poets more excellent have lived before me, and others will come after me. But that in my century I am the only person who knows the truth in the difficult science of colours – of that, I say, I am not a little proud, and here I have a consciousness of a superiority to many.’