I08 PROCEEDINGS OF THE CANADIAN INSTITUTE. 



is produced by the superposition of two spectra, so that the red and violet rays act 

 together, and so give purple. The presence of purple, therefore, proves nothing which 

 could reflect on the ordinary theory, but the absence of green is of more significance. 

 If green is a constituent of white light, why is it absent ? Where is the green ? 

 If we answer, Just where the purple is in the ordinary spectrum, we must undertake 

 a thorough discussion as to the basis of the contention that green is a constituent 

 of white light while purple is not. The fact is, if we prevent the rays of the ends 

 of the spectrum interacting we lose purple, and if we prevent the rays of the middle 

 of the spectrum interacting we lose green. The absence of both of these colours 

 from the spectra seems to be rather a property of the means used in each case than 

 of white light. In white light every wave acts at the same point, while in the 

 longitudinal arrangement of the colours, as in a spectrum, we prevent this; but 

 while allowing the neighbouring waves to act together we deprive the waves of 

 ends of the spectrum altogether of this possibility. Hence, Dr. Kirschmann 

 contends, the absence of these colours in each case. He suggests, therefore, 

 that the theory be modified and stated as follows : " Colour-quality is a function of 

 the superposition of wave lengths, so that to every qualitative difference in spectral 

 colours corresponds a difference in the mode of superposition.* 



This position goes back to the psychology of the question. If purple were 

 found to play an exceptional role in our colour sensations there might be grounds 

 for rejecting these conclusions. But if, as is the case, purple be found to obey the 

 same laws which all other colour sensations follow, there is no reason whatever 

 for regarding it in any peculiar light. It is a colour quite as much as any other. 

 There is, therefore, no a priori reason for rejecting it from the list of pure colours. 

 If, however, it must be rejected in the case of the ordinary spectrum, surely green 

 must be rejected in the case of the inverted spectrum from the list of the constituents 

 of white light, and both for the same reason. 



The third question discussed was along the line of the general psychology of 

 colour. 



Experiments were made, showing that colour sensation could occur when 

 physically there was no light of the specific colour present, e.g., as in contrast 

 phenomena. 



The manifoldness of our colour sensations was also illustrated by a geometrical 

 construction known as " the colour cone," and by means of rotating discs, showing 

 transitions in shades, tints and saturations of colour. 



The fact that, from the psychological standpoint, there is no reason to speak of 

 fundamental colours was discussed, and the significance of the colour theory of 

 Prof. Wundt was pointed out. Owing to modifications made in connection with 

 this theory recently by Dr. Kirschmann, and in consideration of the modifications 

 suggested to the physical colour theory by the same scientist, it seems proper to 

 give the theory the name of the Wundt-Kirschmann Colour Theory. 



*" Colour saturation and its quantitative relations." — American Journal of Psychology, Vol. VII., No. 3. 



