900 



NATURE 



[December 22, 1923 



Dr. Edridge-Green fu 

 written several papers ' 

 theory, l>iit impiic- ' 

 many winch thouKli 

 atic theory are foun 

 strongly adverse to 

 support the theory, but mh 1 



have 

 iiiatic 

 : (■ iijUuilcd among 

 pport the trichrom- 

 iimnation to give facta 

 !s true that my papers 

 ufercnce that they were 

 written for that purpose is incorrect. The papers are 

 discussions of experimental researches on the effects of 

 fatigue of the eye, and the results, usually KJven in the 

 form of persistency curves, are set fortJi independent of 

 any theory. The experimental fact, disclosed by the 

 curves, that the disturbances inflm cd l.\ fatiiiue in 

 the eye invariably affected the re<l \ Jolet 



colours. < ould nnt in my judKmcnt 1- m any 



ot licr '. iiport of ■ 



ir, I II also (|ii' ' 



<>l luy papers lu which 1 n N r w 



III lit ully urii>ing 

 lidiii tlie visiial romplexity ot tlic part ot the spectrum 

 iKtwccn l)w i MiLjths 0-470M and o'570M. which 



UK lii(l( s 1 1 where the sensation curves of 



Ah i ions, and those 



of ^ part of the 



spn iiii;ii 1. I i.niph \ oiiiy oil live trKiiromatic theory, 

 whih' on Ins it is (|nite simple, and that my results 

 therefore " sliould be as stated," or, in other words, 

 accord witli Ins theory. My former experiments, and 

 more espei i ill\ those very recently published, which 

 sliou iiow loloiir vision in one eye is affected by reflex 

 actuju arising Irom fatigue in the same eye and in the 

 other, prove that the spectrum in its physiological 

 action is exactly as complex as the sensation curves 

 indicate it to be. I find a transition point, or, as it 

 now seems better to term it, an equilibrium point or 

 colour, corresponding to each of the intersections of the 

 sensation curves. These facts are experimental, and 

 certainly support the trichromatic theory in the most 

 detailed and explicit manner. Indeed it was the 

 occurrence of these complex intersections of the 

 trichromatic sensation curves that enabled me to 

 predict and later to discover these equilibrium colours. 



The difficulty that Dr. Edridge-Green quotes from 

 my paper regarding vision in the green has now been 

 removed by further investigations which are described 

 in a paper, " On Reflex Visual Sensations," recently 

 published in the Journal of the Optical Society of 

 America, August 1923. The solution is remarkably 

 concordant with Prof. Peddie's conclusion contained 

 in his recent book, which had not been published when 

 that paper was written, and also in his letter in 

 Nature of October 27, p. 621, that in the visual 

 process we have a double set of three variables, one 

 of which arises from the internal action of the visual 

 apparatus. This conclusion to which Prof. Peddie 

 has come, from the interpretation of many phenomena 

 of colour vision, accords with my own experiments on 

 reflex sensations, though I would express it as a set of 

 three variables acted upon by two separate and 

 opposite stimulations, direct and reflex, the former 

 acting to fatigue or depress the sensations, and the 

 latter to enhance them. The double stimulation of 

 the three sensations seems to be the necessary funda- 

 mental connecting principle in colour vision. By its 

 employment many facts which were admittedly 

 difticult to reconcile with the trichromatic theory are 

 now seen to be completely in harmony with it. 



By the discovery of reflex visual action upon the 

 colour sensations it now seems possible legitimately 

 and confidently to establish the trichromatic theory 

 of colour vision upon the broad physiological founda- 

 tions so securely laid bv the researches of Sir Charles 

 Sherrington. " Frank Allen. 



Department of Physics, . 

 University of Manitoba, 



Winnipeg, Canada. 



Prof. Peddie seems to suggest that no one under 

 stands the trichromatic theory but himself. I resent 

 his remarks in this com and for this reason 



unless some one else joii liscussion, this is \w\ 



final letter 



The trit ! theory, which is very simple, lia 



been thoroiiKiM> understood by phynologists sine 

 it was propounded. In former times most physicist < 

 like Prof. Peddie, overlooked the physiological a«TM-. • 

 of the question, but this is not the case wi 

 physicists of the present day. as inav be seen 1 

 writings of Sir Oliver LxKlgt Porter, in 



Houstoun, Prof. Andrado, Dr. C. 1 



Martin, and others irily one <.! 



physiology and not lem on tli' 



functions of three variable.-. ,)'>•■•, ■■. . ar' 



limited to one set of fundai .Morui.i! \; ii,;i 



for one person. A ni' .e live and -si.-; 



toes on one foot at the Now each set <.t 



facts requires a differei tundamentals 



makes the theory quit*- <•. I.^t us co: 



for exam p] I *' "^ mdanicm 1 t Abney and ijurcn. 

 Abney gi\ ' 1 sensation ;!rcted by light of 



all wave-lcii^i '•■■•-rh give,-, the red sensation as 



affected by lij.^! 760 mm to ^555 mm, with otlur 



points of aifferci.v^v. ;!)ney gives X548 mm as stimulat- 

 ing the fundamentals, m sensation luminosities in the 

 following proportions : red sensation m^-- I'n-pn 

 sensation 35 "6, and blue sensation i 



writing on the same subiect. n ; 1- 



thesis instead of fatigue - results ;■ 



"The general conclu l)e drawn mc 



work is therefore that minutliesis due to one colour 

 does not alter the luminosity of another colour to a 

 degree differing appreciably from that in which it is 

 altered itself. In other words, the change in sensi- 

 tivity to brightness occasioned by stimulation of the 

 retina is independent of the wave-length constitutions 

 of the minuthetic and of the reacting lights. This 

 seems to imply that tlie Itiininosity function is not 

 essentially linked with the color or chromatic function 

 and stands in contradiction to the views of Abney, 

 Ives, and others who treat luminosity as the sum of the 

 primai-y colour values of any stimulus. The present 

 results appear also to conflict with experimental data 

 along similar lines published by Abney and by Burch, 

 so that further study of the problem would seem to 

 be required on a larger number of subjects." 



These results are in a complete agreement with 

 those of Prof. A. W. Porter and myself. (See Pro- 

 ceedings Royal Society, 191 2, and the " Physiology of 

 Vision," page 248.) Prof. Peddie's explanations are 

 not explanations on the trichromatic theoiA' : in the 

 first he introduces a fact which can only be explained 

 on my theory ; in the second and third he gives no 

 explanation. The positive after-image of red dis- 

 appears before that for green, therefore on the trichro- 

 matic theory, if yellow be compounded of red and 

 green, red having disappeared, the p>ositive after- 

 image of yellow should change to green, which •> ' 

 not. F. W. Edridge-Gk 



London, December 8. 



NO. 2825, VOL. 112] 



The Optical Spectrum of Hafnium. 



In a letter to X-mtre of October 27, p. 618. in 

 which we gave a complete list of the lines belonging 

 to the hafnium spectrum between 2300 and 3300 

 A.U., we announced a detailed examination of the 

 remaining part of the spectrum which can be obtained 

 photographically. The result of this examination 

 will be found in a paper, now in the press, which will 

 appear shortly in the Math. Phys. Proceedings of 

 the Royal Danish Academy. This paper contains 



