following:—Let a tin plate painted with the prismatic colours in stripes be placed in an empty cubical vessel, so that from the spectator's point of view the colours may be just hidden by the rim. On pouring water into this vessel, all the colours become visible in the same degree; whereas, it was contended, if the Newtonian doctrine were true, some colours would be apparent before others.—Historischer Theil, p. 434.
Such are the arguments and experiments adduced by Goethe on this subject; they have all probably been answered. In his analysis of Newton's celebrated Experimentum Crucis, he shows again that by reversing the prismatic colours (refracting a dark instead of a light object), the colours that are the most refrangible in Newton's experiment become the least so, and vice versâ.
Without reference to this objection, it is now admitted that "the difference of colour is not a test of difference of refrangibility, and the conclusion deduced by Newton is no longer admissible as a general truth, that to the same degree of refrangibility ever belongs the same colour, and to the same colour ever belongs the same degree of refrangibility."—Brewster's Optics, p. 72.
NOTE Q—Par. 387.
With the exception of two very inconclusive letters to Sulpice Boisserée, and some incidental observations in the conclusion of the historical portion under the head of entoptic colours, Goethe never returned to the rainbow. Among the plates he gave the diagram of Antonius de Dominis. An interesting chapter on halos, parhelia, and paraselenæ, will be found in Brewster's Optics, p.