September 9, 1922] 



NA TURE 



359 



may conveniently refer to the heavy pendulums by 

 the names of colours, thus " red," if of the same 

 frequency as the " red " responder rR, etc. 



Tried in this way we find the simultaneous use of 

 blue and yellow drivers does not give the response 

 appropriate to green but gives white, i.e. all the three 

 responders are set in motion. On reference to the 

 diagram it is possible to see why this follows. The 

 blue driver (representing blue light) is intermediate in 

 frequency between the responders Gg and Vv, and so 

 excites both. The yellow driver has a frequency be- 

 tween those of Rr and Gg and excites both. But the 

 simultaneous drives on the green responder will inter- 

 fere by being often much out of phase, so the response 

 of the green responder is no more than those of the 

 violet and red, indeed the last-named often prepon- 

 derates. It should be noted that in the above test the 



colours used as stimuli were both such as had no 

 appropriate responder postulated. 



For red and green the case is different ; each has an 

 appropriate responder provided in the hypothesis, and 

 each is affected by the corresponding stimulus when 

 red and green pendulums are used as drivers. But 

 when a yellow driver is used, i.e. a pendulum inter- 

 mediate in frequency between the red and green re- 

 sponders, they are both affected as when the separate 

 red and green drivers were in use. Thus, on the hypo- 

 thesis under examination, the naked eye would mistake 

 a true addition of red and green for a yellow. And this 

 is just what happens when the experiment is tried. 



This is quite different from what occurs in hearing, 

 where two notes like C$ and F# when sounded 

 simultaneously are not mistaken for any single inter- 

 mediate note. This distinction is, however, adequately 



explained in the two hypotheses dealt with in this 

 article on vision and the previous one on audition 

 (see Nature, September 2, p. 316). In the case of 

 vision only three heavily damped responders are postu- 

 lated in the single octave, whereas for hearing twelve 

 lightly damped responders were postulated for each 

 octave. The latter secures the finer analysis of 

 which the ear is known to be capable, whereas the 

 former agrees with the known lack of spectrum analysis 

 in the eye. It still leaves power to discriminate twenty 

 or thirty distinct colours in the whole spectrum, how- 

 ever, for if one pendulum CD be used as stimulus it may- 

 be changed gradually in length by twenty or thirty 

 steps from the frequency corresponding to the violet 

 responder to that of the red one, and at each adjust- 

 ment the relative amplitudes of the three responders 

 are appreciably different. 



Subsidiary Hypothesis. — To meet the 

 cases of colour blindness, one or more 

 of the three responders is supposed to 

 be absent or abnormal in frequency or 

 damping. This opens out a wide field 

 of possibilities. 



To explain the time effects (the tenth 

 of a second needed to acquire or lose 

 the full visual sensation) a subsidiary 

 hypothesis is put forward. The vibra- 

 tory response is supposed only to 

 initiate the process of vision by starting 

 some changes of a physiological or 

 chemical nature which in turn affect 

 the nerves, these changes being, 

 however, quantitatively dependent 

 upon their vibratory initiation. 

 When the light stimulus ceases 

 the vital activities are assumed to restore the 

 changed materials of the retina to their normal 

 states. Both changes are supposed to occupy 

 something of the order of a tenth of a second. 



The object of the present article was simply to show 

 whether a syntonic hypothesis is adequate to explain 

 the chief facts of vision. The conclusion is in the 

 affirmative. But the hypothesis is not thereby estab- 

 lished. We can only say that, if the hypothesis be 

 true, colour vision would be, in the main, as we now 

 experience it. 



To suggest the exact nature of a probable or possible 

 mechanism to carry out this syntonic hypothesis is 

 another matter and beyond the scope of the present 

 article. It was, however, discussed by Sir Oliver Lodge 

 at the Bournemouth meeting of the British Association 

 in 1919. 



Obit 



Prof. J. A. Pollock, F.R.S. 



PROF. JAMES ARTHUR POLLOCK, professor of 

 physics in the University of Sydney since 1899, 

 who died after a short illness on May 24. at the age of 

 fifty-seven years, was a fine physicist and a man of ex- 

 ceptionally high, loyal, and unselfish character. He was 

 born in or near Cork, and was educated at the Manchester 



NO. 2758, VOL. I 10] 



u ary. 



Grammar School and the Royal University of Ireland, 

 taking an engineering degree. He and his brother, Hugh 

 Pollock (they were inseparable), were intended to enter 

 some linen-manufacturing business in which his family 

 were interested ; but this proving a disappointment in 

 some way, the young men with their father and some 

 other members of their family went to Sydney about 

 1884. Arthur Pollock obtained an appointment at the 



