14 DeWitt B. Brace, 



— ^y 

 a. ii =A-e 



2a 



Curve Ij represents the distribution of energy according to 

 la. after the amplitude of a wave corresponding to .80 in the 

 diagram has been diminished .01 of its original value. Curve 

 lo and IL, represent this distribution according to la. and 

 lla. respectively after a diminution in amplitude of .10 of its 

 original value for the same wave. 'The law representing 

 absorption according to III. would be a curve between these 

 two. The curve Ai^ represents what the normal distribution 

 would be if no energy had been absorbed and the amplitude 

 had been uniformly diminished by . 10. From these curves we 

 are able to determine the proportion of the rays lacking in the 

 different parts of the spectrum which would when added give 

 the original spectrum. Thus from Ij of the red rays about 

 .006 are lacking ; of the orange and yellow, about .020 ; of the 

 green, nearly .030 ; and of the violet, about .050. In the same 

 Vv^ay for curve I2, about .06 of the red rays would be lacking, 

 ,15 of the yellow, .20 of the green, and about .50 of the violet. 

 If the law of absorption is according to curve IL, about .03 of 

 the red would have been absorbed to .06 of the yellow, nearly 

 .10 of the green, and nearly .40 of the extreme violet. It is 

 thus evident that the greater the absorption, the redder the 

 spectrum will appear. 



Aubert has shown that less than one per cent of red mixed 

 with white is perceptible. For sufficient intensity, curve Ij 

 would be within this limit, so that a hue near the orange-red 

 would be perceptible. Either lo or 11^ would evidently give 

 a very perceptible reddish tinge. Thus from the hue it is 

 possible, for a given intensity, to determine the total loss in 

 intensity and the diminution in amplitude. In the curve Ii 

 the amplitude of the yellow rays has been diminished from 

 two to three per cent. In curves I2 and IL the diminution has 

 been about twenty per cent and fifteen per cent respectivel3\ 



14 



