(_c._) The process of bluing steel is a fine illustration of Goethe’s theory. The steel is polished so that it reflects light like a mirror. On placing it in the charcoal furnace a film of oxydization begins to form so that the light is reflected through this dimming medium; this gives a straw color. Then, as the film thickens, the color deepens, passing through red to blue and indigo. (_d._) The prism is the grand instrument in the experimental field of research into light. The current theory that light, when pure, is composed of seven colors, is derived from supposed actual verifications with this instrument. The Goethean explanation is by far the simplest, and, in the end, it propounds a question which the Newtonian theory cannot answer without admitting the truth of Goethe’s theory. II.—The phenomenon of refraction is produced by interposing different transparent media between the luminous object and the illuminated one, in such a manner that there arises an apparent displacement of one of the objects as viewed from the other. By means of a prism the displacement is caused to lack uniformity; one part of the light image is displaced more than another part; several images, as it were, being formed with different degrees of displacement, so that they together make an image whose edges are blurred in the line of displacement. If the displacement were perfectly uniform, no color would arise, as is demonstrated by the achromatic prism or lens. The difference of degrees of refraction causes the elongation of the image into a spectrum, and hence a mingling of the edges of the image with the outlying dark surface of the wall, (which dark surface is essential to the production of the ordinary spectrum). Its _rationale_ is the following: (_a_) The light image refracted by the prism is extended over the dark on one side, while the dark on the other side is extended over it. (_b_) The bright over the dark produces the blue in different degrees. The side nearest the dark being the deepest or violet, and the side nearest the light image being the lightest blue. (_c_) On the other side, the dark over light produces yellow in different degrees; nearest the dark we have the deepest color, (orange approaching to red) and on the side nearest the light, the light yellow or saffron tint. (_d_) If the image is large and but little refracted (as with a water prism) there will appear between the two opposite colored edges a colorless image, proving that the colors arise from the mingling of the light and dark edges, and not from any peculiar property of the prism which should “decompose the ray of light,” as the current theory expresses it. If the latter theory were correct the decomposition would be throughout, and the whole image be colored.