ARTICLE I. Modifications produced by Coloured Lights. (261.) These modifications result from coloured rays emanating from any source whatever, falling upon a coloured surface, which is at the same time lighted by diffused daylight. (262.) The following observations have been made by partially exposing coloured stuffs to the sun's rays transmitted through coloured glass. The portion of stuff protected from these rays was lighted by the direct light of the sun. It is important to remark, that the portion of stuff which received the action of the coloured rays being exposed to diffused daylight, reflected also rays of that light which it would have reflected in case it had been protected from the influence of the rays transmitted to it through coloured glasses. (263.) 1°. Modifications produced by Red Light. When Red rays fall upon a Black stuff, it appears of a Purple-Black, deeper than the rest, which is lighted directly by the sun. Red rays falling upon a White stuff, make it appear Red. Red rays falling upon a Red stuff, make it Red rays falling upon an Orange-coloured Red rays falling upon a Green stuff, produce Red rays falling upon a light Blue stuff, make appear Violet. it Red rays falling upon a Violet stuff, make it appear Purple. SAMOLE OXFORD MUSEUM (264.) 2°. Modifications produced by Orange Light. Orange rays falling upon a Black stuff, make Orange rays falling upon an Orange stuff, Orange rays falling upon a Red stuff, make it appear Scarlet. Orange rays falling upon a Yellow stuff, make it appear Orange-Yellow. Orange rays falling upon a Green stuff, make it appear of a Yellow-Green, if the Green is light; and of a rusty-Green, if it is deep. Orange rays falling upon a Blue stuff, make it appear of an Orange-Grey, if the Blue is light; and of a Grey in which the Orange is less vivid, if it is deep, which is not the colour given to a black stuff by the same Orange rays. Orange rays falling upon a dark Indigo-Blue stuff, make it appear of an Orange-Maroon. Orange rays falling upon a Violet stuff, make it appear of a Red-Maroon. (265.) 3°. Modifications produced by Yellow Light. Yellow rays falling upon a Black stuff, make it appear of an Olive-Yellow. Yellow rays falling upon a White stuff, make it appear of a light Yellow. Yellow rays falling upon a Yellow stuff, make it appear (relatively to the part lighted by the sun) of an Orange-Yellow colour. Yellow rays falling upon a Red stuff, make it appear Orange. Yellow rays falling upon an Orange stuff, make it appear more Yellow than the part lighted by the sun. Yellow rays falling upon a Green stuff, make it appear Yellow-Green. Yellow rays falling upon a Blue stuff, make it appear Green-Yellow, if it is light, and of a Green-Slate if it is deep. Yellow rays falling upon a deep Indigo stuff, make it appear of an Orange-Yellow. Yellow rays falling upon a Violet stuff, make it appear Yellow-Maroon. (266.) 4°. Modifications produced by Green Light. Green rays falling upon a Black stuff, make it appear of a Green-Brown. Green rays falling upon a White stuff, make it appear Green. Green rays falling upon a Green stuff, make it appear more intense and brilliant. Green rays falling upon a Red stuff, make it appear of a Brown. Green rays falling upon an Orange stuff, make it appear of a faint Yellow, a little Green. Green rays falling upon a Yellow stuff, make it appear of a very brilliant Yellow-Green. Green rays falling upon a Blue stuff, make it appear Greener, according to its depth. Green rays falling upon a dark Indigo stuff, make it appear a dull Green. Green rays falling upon a Violet stuff, make it appear of a Bluish-Green-Brown. (267.) 5°. Modifications produced by Blue Light. Blue rays falling upon a Black stuff, render it of a Blue-Black, deeper than the part lighted by the sun. Blue rays falling upon a White stuff, make it appear Blue. Blue rays falling upon a Blue stuff, render the colour more vivid than the part lighted by the sun. Blue rays falling upon a Red stuff, make it appear Violet. Blue rays falling upon an Orange stuff, make it appear of a Brown having an exceedingly pale tint of Violet, if the glass transmits Violet rays with the Blue. Blue rays falling upon a Yellow stuff, make it appear Green; if the rays are transmitted by a deep Blue glass, coloured with oxide of cobalt, the stuff will appear of a Brown, having a Violet tint, less apparent if the light is vivid. Blue rays falling upon a Green stuff, make it Blue rays falling upon a deep Indigo stuff, (268.) 6°. Modifications produced by Violet Light. Violet rays falling upon a White stuff, make it appear Violet. Violet rays falling upon a Violet stuff, make it appear of a deeper Violet. Violet rays falling upon a Red stuff, make it appear of a Red-Violet-Purple. Violet rays falling upon an Orange stuff, make appear of a light Red. it Violet rays falling upon a Yellow stuff, make it appear Brown with an exceedingly pale tint of Red. Violet rays falling upon a Green stuff, make it appear light Purple. Violet rays falling upon a Blue stuff, make it appear of a fine Violet-Blue. Violet rays falling upon a dark Indigo stuff, make it appear of a very deep Violet-Blue. (269.) It is understood that to represent the preceding phenomena correctly we must take into account: the facility with which coloured light penetrates every kind of glass the colour more or less intense of the stuff upon which the coloured light falls-and the kind of scale to which the coloured stuff and that of the transmitted coloured light respectively belong. ARTICLE 2. Modifications produced by two Lights of different Intensity. (270.) I shall distinguish two modifications of this kind. 1. The modification produced by the light of the sun falling upon one part of the surface of a coloured body, while the other part is lighted by diffused daylight. 2. The modification produced when two parts of the same object are unequally illuminated by diffused light. Ist MODIFICATION. An Object lighted partly by the Sun, and partly by diffused Daylight. (271.) To observe this kind of modification properly we must extend upon a table exposed to the sun a piece of stuff, A B, 2 inches square (Plate III. fig. 1.), and place in the middle a piece of Black wire f,f'; then put parallel to this wire, and in the middle, between A and B, two blackened iron bands, e, e', and g, g', of about 3ths of an inch in width. The extremity, g', is fixed upon a perpendicular plane, h, h', of 1 andths of an inch in length, and sufficiently high, so that ff, being in the plane of the direction of the solar rays, the plane h, k, covers exactly with its shadow all the part B of the stuff. (272.) 1°. If the stuff is Red, the lighted portion A is more Orange or less Blue than the part B, which is in shade; and the portion a is more Orange than the portion a', as the portion b is Bluer or more Crimson than the portion b. (273.) 2°. If the stuff is Orange, the lighted part is more Orange or less Grey than the part which is in the shade, and the portion a is deeper, |