ADDRESS. 19 



by the most elementary forms of eye only in chiaroscuro, that afterwards 

 some colours were distinguished, eventually all. As regards hearino- 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 Ctenopliora — 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 traceable. 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 serves as the guide to our bodily move- 

 ments. 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 

 inca.pable 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 deter, 

 mined is whether the latter represents a ' specific energy ' 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 lio-ht, but 

 whether we possess a separate faculty by which we judge of lio-ht and 

 shade — a question which, although we have derived our knowledge of it 

 chiefly from physical experiment, is one of eye and brain, not of wave- 

 lengths or vibration-rates, and is therefore essentially physiological. 



There is a Grerman proverb which says, 'Bei Nacht sind alle Katzen 

 grau.' The fact which this proverb expresses presents itself experiment- 

 ally when a spectrum projected on a white surface is watched, while the 



' Verworn, ' Gleichgewicht u. Otolithenorgan,' Pjtiiger's Arcldv, vol. 1. p. 423 ; 

 also Ewald's researches on the Labyrinth as a Sense-organ ( Ueher das Endorgan 

 des Nervus octavtts, Wiesbaden, 1892). 



c 2 



