140 ANNUAL OF SCIENTIFIC DISCOVERY. 



white pencil have been bent, cadi ha.s been bent at a different angle, the 

 ml most, and the blue least. When, therefore, they come out of the drop, 

 tin- ifl rays are quite separated from the blue, and when the beam reaches 

 ir> destination, the various colors enter the eye separately, forming a line of 

 variouslv colored light, the upper part red and the lower part blue, instead 

 t>i a mere point of white light, as the ray would have appeared if seen before 

 it entered the drop. The eye naturally refers each part of the ray to the 

 place from whence it appears to come, and thus, with a number of drops 

 falling and the sun not obscured, a rainbow is seen, which represents part of 

 a number of concentric circular lines of color, the outermost of which is red, 

 the innermost violet, and the intermediate ones we respectively name orange, 

 yellow, green, blue, and indigo. 



It has also been found, by careful experiment, that these are not all pure 

 colors, most of them being mixtures of some few that are really primitive 

 and pure, and necessarily belong to solar light. It is these, mixed in due 

 proportion, which make up ordinary white light, which is the only kind seen 

 when the sun's rays have not undergone this sort of decomposition, or sepa- 

 ration into elements. The actual primitive colors are generally supposed to 

 be red, yellow, and blue, and much theoretical as well as practical discussion 

 has arisen as to how these require to be mixed, what proportion they bear 

 to each other in their power of impressing the human eye, and many other 

 matters, for which we must refer to Mr. Field, Mr. Owen Jones, and others, 

 who have studied the subject and applied it. 



In a general way it is found convenient to remember, or rather to assume, 

 that three parts of red, five parts of yellow, and eight parts of blue, form 

 together white, and, therefore, that the pencil of white light contains three 

 rays of red, five of yellow, and eight of blue. To produce the other prismatic 

 colors, we must mix red with a little yellow to form orange; yellow with 

 some blue to form green; much blue with a little red to form indigo, and a 

 little blue with some red to form violet. In performing experiments on color 

 it is convenient, instead of a drop of water, to substitute a prism of glass in 

 decomposing the rays of light. We may thus produce at will a convenient 

 image, called a prismatic spectrum, which, when thrown on a wall, is a broad 

 band of colored lights, having all the tints of the rainbow in the same order. 

 Looking at this image, the red is at the top and the violet at the bottom, 

 and it may be asked, How does the red get amongst the blue to form violet, 

 if the red rays are bent up to the top of the spectrum? The answer is, that 

 a quantity of white light not decomposed, and a part of all the color-rays, 

 reach all parts of the spectrum, however carefully it is sheltered, but that so 

 many more red rays get to the top, so many more of the yellow to the 

 middle, and so many more blue to where that color appears most brilliant, 

 that these are seen nearly pure, whilst where the red and yellow or yellow 

 and blue mix they produce distinct kinds of color, and where the blue at the 

 bottom is faint, and some of those red rays fall that do not reach the red 

 part of the spectrum, the violet is produced. In point of fact, therefore, all 

 the colors of the spectrum, as seen, are mixtures of pure colors with white 

 ILht, while all but red are mixtures of other pure colors with some red and 

 some yellow, as well as white. Primitive and pure colors, therefore, are not 

 obtained in the spectrum, and a question has arisen as to which really de- 

 serve to be called pure; Dr. Young upholding green against yellow, and even 

 regarding violet as primitive, and blue a mixed color. A consideration of 



