714 Messrs. H. E. Ives and E. F. Kingsbury on the 



in the " transmitter 9> or in the ultimate " receiver " the 

 separate impressions are instantaneously added, then the 

 resultant is similar to the case shown in fig. 4, namely, an 

 outstanding flicker. This represents the result o£ taking two 

 colours on a vertical line on fig. 1 as a-c. 



Now take another possible case, that where the two colours 

 are chosen of such brightness that their fluctuating sensation 



Fig;. 6. 





/S 



/ \ /■? 







Va 



Uesult of alternating two colours of unequal brightness and unequal 

 relative amplitude of fluctuation, so chosen that their summation is of 

 constant value. Referring to fig. 1, this means that neither the intensity 

 b nor c will alternate with a to produce no flicker. Some intermediate 

 intensity is called for. This is the case of the flicker photometer. 



curves have the same contour or ratio of maximum to mini- 

 mum. This, is equivalent to taking the two points on the 

 horizontal line a-b. In this case one colour is brighter than 

 the other, as indicated by the scale of abscissae. The re- 

 sultant is again a flicker, fig. 5. It is then clear that neither 

 the alternation of two equally bright colours, nor of two 

 chosen in those proportions for which each has the same 



