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.) 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. 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. It was clear to Goethe that to trace the law of the genesis of colour in nature by reading her phenomena, he must keep a look-out for occurrences of colours which satisfied the conditions of the Ur-phänomen, as he had learned to know it. This meant that he must ask of nature where she let colours arise out of light and darkness in such a way that no other conditions contributed to the effect.