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.'

We find ourselves faced here with an instance of the problem,
'Discovery or Manufacture?' dealt with by Eddington in the manner
described in our previous chapter. This very instance is indeed used by
Eddington himself as a case in which the answer is definitely in favour
of 'manufacture'. Nevertheless, Eddington complains, experts, in spite
of knowing better, keep to the traditional way of speaking about the
spectral colours as being originally contained in the light. 'Such is
the glamour of a historical experiment.'3 It is for the same reason
that Goethe's discovery continues to be unrecognized by the majority of
scientists, who prefer, instead of examining the question for
themselves, to join in the traditional assertion that 'Goethe never
understood Newton'.