September 14, 1893] 



NATURE 



469 



It is these lines of influence which interest the physiologist. 

 The structure of the visual apparatus affords us no clues to trace 

 them by. The most important fact we know about them is that 

 they must be at least three in number. 



It has been lately assumed by some that vision, like every other 

 specific energy, having been developed progressively, objects 

 were seen by the most elementary forms of eye only in chiaros- 

 curo, that afierwardsjsome colours were distinguished, eventually 

 all. As regards hearing it is so. The organ which, on structural 

 grounds, we consider to represent that of hearing in animals low 

 in the scale of organisation — as, e.g., in the Ctenophora — has 

 nothing to do with sound, ^ but confers on its possessor the 

 power of judging of the direction of its own movements in the 

 water in which it swims, and of guiding these movements 

 accordingly. In the lowest vertebrates, as, e.g., in the dogfish, 

 although the auditory apparatus is much more complicated in 

 structure, and plainly corresponds with our own, we still find 

 the particular part which is concerned in hearing scarcely trace- 

 able. All that is provided for is that sixth sense, which the 

 higher animals also possess, and which enables them to judge 

 of the direction of their own movements. But a stage higher 

 in the vertebrate series we find the special mechanisms by 

 which we ourselves appreciate sounds beginning to appear — 

 not supplanting or taking the place of the imperfect organ, but 

 added to it. As regards hearing, therefore, a new function is 

 acquired without any transformation or fusion of the old into it. 

 We ourselves possess the sixth sense, by which we keep our 

 balance and which selves as the guide to our bodily movements. 

 It resides in the part of the internal ear which is called the 

 labyrinth. At the same time we enjoy along with it the 

 possession of the cochlea, that more complicated apparatus by 

 which we are able to hear sounds and to discriminate their 

 vibration-rates. 



As regards vision, evidence of this kind is wanting. There 

 is, so far as I know, no proof that visual organs which are so 

 imperfect as to be incapable of distinguishing the forms of 

 objects, may not be affected differently by their colours. Even 

 if it could be shown that the least perfect forms of eye possess 

 only the power of discriminating between light and darkness, 

 the question whether in our own such a faculty exists separately 

 from that of distinguishing colours is one which can only be 

 settled by experiment. As in all sensations of colour the 

 sensation of brightness is mixed, it is obvious that one of the 

 first points to be determined is whether the latter represents a 

 "specificenergy " or merely a certain combination of specific 

 energies which are excited by colours. The question is not 

 whether there is such a thing as white light, but whether we 

 possess a separate faculty by which we judge of light and shade 

 —a question which, although we have derived our knowledge 

 of It chiefly from physical exjeriment, is one of eye and brain, 

 not of wave-lengths or vibration-rates, and is therefore essen- 

 tially physiological. 



There is a German proverb which says, " Bei Nacht sind alle 

 Katzen grau. The fact which this proverb expresses presents 

 Itself experimentally when a spectrum projected on a white 

 siirface IS watched, while the intensity of the light is gradually 

 diminished. As the colours fade away they become indistin- 

 guishable as such, the last seen being the primary red and 

 ^''.""- ?'"a"y 'hey also disappear, but a gray band of light 

 still remains, of which the most luminous part is that which 

 before was green.- Without entering into details, let us con- 

 sider what this tells us of the specific energy of the visual 

 apparatus. Whether or not the faculty l)y which we see gray 

 in the dark is one which we possess in common with animals of 

 imperfectly dt^veloped vision, there seems little doubt that there 

 are individuals of our own species who, in the fullest sense of 

 the expression, have no eye for colour ; in whom all colour 

 sense is ab.ent ; persons who inhabit a world of gray seeing all 

 things as they might have done had they an J their ancestors 

 always lived nocturnal lives. In the theory of colour vision 

 as It IS commonly stated, no reference is made to such a faculty 

 as we are now discussing. 



I'rof. Hering, whose observations as to the diminished 

 spectrum I referred to just now, who was among the first to 

 -ubject the vision of the totally colour-blind to accurate exam- 



>erwoni, " Gleichgewicht u. Otolithenorgan," P/lttgers Arthiv. vol 



( I cber dar, I. ndr.rgan d.s Nervus < ctavus," Wiesbaden. iBgj). 



„, ""-ng. Untersuch. enra total Farbenblinden," Pjhlter-, Arch, vol 



, 'o9'i P' 503- ' 



NO. 1246, VOL. 48] 



ination, is of opinion, on that and on other grounds, that the- 

 sensation of light and shade is a specific faculty. Very recently 

 the same view has been advocated on a wide basis by a dis- 

 tinguished psychologist. Prof. Ebbinghaus.' Happily, as 

 regards the actual experimental results relating to both these 

 main subjects, there seems to be a complete coincidence of ob- 

 servation between observers who interpret them differently. 

 Thus the recent elaborate investigations of Captain Abney''' 

 (with General Festing), representing graphically the resulis of 

 his measurements of the subjective values of the different parts 

 of the diminished spectriim, as well as those of the fully illu- 

 minated spectrum as seen by the totally colour-blind, are in the 

 closest accord with the observations of Hering, and have, more- 

 over, been substantially confirmed in both points by the 

 measurements of Dr. Konig in Helmholtz' laboratory at 

 Berlin.' That observers of such eminence as the three persons 

 whom I have mentioned, employing different methods and with 

 a different purpose in view, and without reference to each 

 other's work, should arrive in so complicated an inquiry at 

 coincident results, augurs well for the speedy settlement of this 

 long-debated question. At present the inference seems to be 

 that such a specific energy as Ilering's theory of vision postu- 

 lates actually exists, and that it has lor associates the 

 colour-perceiving activities of the visual apparatus, pro- 

 vided that these are present ; but that whenever the intensity 

 of the illumination is below the chromatic threshold — that is, 

 too feeble to awaken these activities — or when, as in the totally 

 colour-blind, they are wanting, it manifests itself independently ; 

 all of which can be most easily understood on such a hypo- 

 thesis as has lately been suggested in an ingmijus paper by 

 Mrs. Ladd Franklin,* that each of the elements of the visual 

 apparatus is made up of a central structure for the sensation of 

 light and darkness, with c jUateral appendages for the sensations 

 of colour — it being, of course, understood that this is a mere 

 di.igrammatic representation, which serves no purposes beyond 

 that of facilitating the conception of the relation between the 

 several " specific energies." 



Experimental Psychology. 



Resisting the temptation to pursue this subject further, I will 

 now ask you to follow me into a region which, a'though closely 

 connected with the subjects we have been considering, is beset 

 with greater difficulties — the subject in which, under the name 

 of Physiological or Experimental Psychology, physiologists and 

 psychologists have of late years taken a common interest — a 

 borderland not between fact and fancy, but between two 

 methods of investigation of questions which are closely related, 

 which here, though they do not overlap, at least interdigitate. 

 It is manifest that, quite irrespectively of any foregone conclu- 

 sion as to the dependence of mind on processes of which the 

 biologist is accustomed to take cognisance, mind mu t be re- 

 garded as one of the "specific energies" of the organism, and 

 should on that ground be included in the subject-matter of 

 physiology. As, however, our science, like other sciences, is 

 limited not merely by its subject but also by its method, it 

 actually takes in only so much of psychology as is experimental. 

 Thus sensation, although it is psychological, and the investi- 

 gation of its relation to the special structures by which the mind 

 keeps itself info; med of what goes on in the outside world, have 

 always been considered to be in the physiological sphere. And 

 it is by anatomical researches relating to the minute structure 

 and to the development of the brain, by observation of the facts 

 of disease, and, above all, by physiological experiment, that 

 those changes in the ganglion cells of the brain and spinal cord 

 which are the immediate antecedents of every kind of bodily 

 action have been traced. Between the two— that is, between 

 sensation and the beginning of action — there is an intervening 

 region which the physiologist has hitherto willingly resigned to 

 psychology, feeling his incompetence to use the only instrument 

 by which it can be explored— that of introspection. This con- 

 sideration enables us to understand the course which the new 

 study (I will not claim for it the title of a new science, regard- 



I Ebbinghaus, " Theorie des Farbenschens,'.' Zeituhr. /. Psychol., vol. 

 v., 1893, p. 145. 



'' Abneyand Festing, Colour Photometry, Part III. Phil. Trans., vol. 

 cl.\x.\ln., A, 1891, p 53T. 



^ K.iiiig '• Ucber den Helligkeitwerth dcr Spectralfarben bei verschicdener 

 absoluter Intcnsii.-it.' Jleitriigc zur Psychologic. &c., "Festschrift Ju H. 

 von Helmholtz, 70, Geburtstage. " 1891, p. 309. 



'Christine Ladd Frankli.n, " Eine neue Theorie der Lichlerapfindungcn," 

 ^eilschr./iir i ,yclioloiif,y<,\ iv., 1B93, p. 211; see also the Proceedings 

 of th<! last Psychological Congress in Loaion, 1892 



