534 STUDIES IN ADVANCED PHYSIOLOGY. 



light. This white light is not a simple light but consists 

 of all the vibrations from the red to the violet. In other 

 words, white light is a concert of all the pitches of light. 

 In music we are able to analyze the individual sounds that 

 go into a complicated harmony, but in light the eye is un- 

 able to make such an analysis, and this combination of all 

 of the colors of the spectrum is perceived as one color and 

 called white. 



By means of a prism it is possible to separate this white 

 light, to analyze it, and get each color by itself. The re- 

 sult of such a procedure is the spectrum familiar to every 

 one, if not in the laboratory, at least in the rainbow. By 

 means of such a prism the colors are strung out, from the 

 red at one end to the violet at the other, and the position of 

 each color is determined by the number of vibrations per 

 second which it has. Commonly we say that in this scale 

 we are able to perceive seven distinct colors. These are: 

 red, orange, yellow, green, blue, indigo, violet. 



Reference to the number of vibrations in red light and 

 violet light shows that violet light is just an octave above 

 red light. It possesses just about twice the number of 

 vibrations, and it is extremely interesting to note that at 

 the violet end the red reappears. In fact, violet is nothing 

 but the blue, with which is mixed a little red, possibly the 

 red of the next octave. It is apparent, therefore, that our 

 range of vision extends over but one octave of colors, from 

 the red at the lower end to the red at the upper end, where 

 it reappears to blend with the blue forming the violet. 

 What the color sensations would be if the range of vision 

 should extend over more than one octave it is entirely im- 

 possible to say. If, however, they should be reproductions 

 of the first octave one can see that nothing would be gained 

 by their presence as far as new colors are concerned, and 

 as the eye is perfectly unable to analyze a compound color, 

 is unable to perceive its inherent harmony, there is but 

 an added reason for the limitation of the range of vision to 

 a single octave. 



