CHAPTER III. 

 SIGHT. 



SEC. 1. ON THE GENERAL STRUCTURE OF THE EYE, 

 AND ON THE FORMATION OF THE RETINAL IMAGE. 



702. IN dealing with the brain we have been incidentally 

 obliged to deal with some of the facts connected with the senses ; 

 but we must now study the details of the subject. And, for the 

 very reason that it is the most highly developed and differentiated 

 sense, it will be convenient to begin with the sense of sight ; we 

 shall find that the study of it throws more liffht on thp 



ERRATUM. 



p. 1492, 1. 15, and elsewhere for 'Graaffian' read ' Graafian. 



.LJUJJ. 



difficulty of distinguishing between the events which are of 

 physical origin, due to changes in the retina and optic fibres, 

 and those which are of psychical origin, due to features of our 

 own consciousness ; for many of our conclusions are based on an 

 appeal to consciousness. We shall find our difficulties further 

 increased by the fact, that in appealing to our own conscious- 



F. 73 



