76 



Prof. F. Allen on Four Transition Points in tlie 



points at the wave-lengths X'olOfM and V-ITO^. Finally, 

 the third fundamental sensation, which must be violet and 

 not blue as many colour-theorists allege, lies between the 

 fourth point of transition at X *420 /jl and the end of the violet. 

 It is to be regretted that this method of investigation does 

 not yet enable us to discover the exact fundamental hues. 

 It is possible that the method of fatiguing the eye with 

 carefully selected pairs of colours at one time, such as I have 

 used in another investigation*, or even with three colours 



Fio-. 20. 



120 



,o NO 



100 



•40/j. 



•55 -60 



Wave Length. 



f?ed<r 



■66 Op. 



■570/UL 



Compound 

 sensat/ons. 



■> Violet 



•470fJ. 



■420/JL 



Compound 

 sensations. 



Fun dam en ta/ 

 red sensation. 



Fundamental 

 green sensation. 



Fundamental 



violet sensation. 



simultaneously, will bring the desired precision. Un- 

 doubtedly such investigations will elicit much new informa- 

 tion on the complex and apparently inexhaustible phenomena 

 of colour- vision. 



One of the most persistent problems in colour-vision is the 

 proper disposition of yellow. In purity of appearance it 

 seems to have quite as much claim as red and green to be 

 regarded as primary in its nature. Indeed, the psychologists 

 quite universally recognize fully the primary quality of^the 

 sensation of yellow. Butthe five persistency curves obtained 

 between the wave-lengths \'660 /* and X'570 //, are identical 



* "Some Phenomena of the Persistence of Vision,'' Phys. Kev. 

 vol. xxviii. (1909). 



