ACCIDENTS BY RAIL AND SEA. 



149 



ferent kinds of objective light in the length of the wave, in the practical 

 course we are pursuing here it is much more convenient to designate 

 them by the efifect they exert on the normal sense of colors. With 

 this explanation we will then proceed to speak of red, green, and violet 

 light, and so on, meaning those ethereal waves which differ in length, in 

 duration of undulations, in refrangibility, etc. 



The easiest and most convenient means of describing the relations 

 existing between the kinds of objective light and the excitability of the 

 different elements, or, in other words, of the different kinds of subjective 

 light, will be to construct a diagram in which the curves indicating the 

 different kinds of light will be traced on an abscissa according to the 

 order in which they are presented in the solar spectrum, and those 

 which indicate the excitability of the respective elements, or rather the 

 intensity of the sensation of colors, will be expressed by the ordinate. To 

 save space, and more easily to comprehend the whole, we have drawn 

 the curves of intensity of the different elements on the same abscissa, 

 which consequently serves for each one of them. 



Figure 1 represents this diagram, showing the normal sense of colors. 

 The spectral colors are here found placed horizontally in the natural 

 order, beginning with the red (E.), and finishing with the violet (V.); 

 the three curves of excitability, namely, 1st, that of the organ perceiv- 

 ing red ; 2d, that of the perceptive organ of green ; and, 3d, that of the 

 organ perceiving violet ; these curves indicate the manner in which the 

 different sj'stems of waves of solar light act on each of the three ele- 

 ments sensible to light. 



FtG. 1. 



According to these curves, the homogeneous red, from the extremity of 

 the spectrum to beyond the orange, affects the perceptive elements of 

 red strongly, in a much less degree those of green, and still less those of 

 violet. From this results the sensation of red, which is transferred more 

 and more into orange in proportion to the increase of the excitation of 

 the perceptive elements of green. Homogeneous yelloio intensely excites, 

 aud almost in the same degree, the perceptive elements of red and green, 

 while only feebly affecting the perceptive elements of violet. Hence, the 

 sensation of yellow, which is a combination of red and green. Green 

 light strongly excites the perceptive elements of green, and very feebly 

 and almost equally the two other elements. Hence, the sensation of 

 green. - Homogeneous blue excites quite strongly and almost equally the 



