12 THE ANNUAL ADDRESS OF THE VICTORIA INSTITUTE. 



able to affect our owu neigliboiirliood ; in the second place, 

 some provision in our own bodies for receiving that in- 

 fluence, and transmitting some sensation to the conscious 

 being. 



In my former address I considered the first of these two 

 subjects ; to-day I mean to confine myself to the second. 

 This second, even by itself is, however, far too Avide for a 

 single address ; selection of some kind is imperatively 

 demanded. Moreover, there are some parts which are 

 accurately known, and may even be made the object of 

 mathematical calculation, while there are others wliich not 

 merely lie beyond our existing knowledge, but beyond any 

 that we can hope to attain to, at least in this life. Wonder- 

 ful as is the construction of the eye in all its parts, so far as 

 relates to the formation of images on the retina it acts 

 simply like an optical instrument, like a telescope or micro- 

 scope, or more correctly like the objective of such an instru- 

 ment, and we may apply our mathematics to tracing the 

 course of the rays through it. On the other hand, even if 

 we knew accurately, which we do not, the nature of the 

 effect which the external agent produces on the ultimate 

 structure of our bodies, there would still remain, shrouded 

 in impenetrable mystery, the nature of the process by which 

 some change in the bodily organism causes a sensation to 

 the conscious being. 



Between these two extremes lies a region which has been 

 to some extent explored, and in whicli a gradual and per- 

 haps at last a very substantial increase to our existing 

 scientific knowledge may be looked upon as probable. The 

 investigation of this region possesses the keen interest 

 which belongs to the discovery of new truths, and the 

 addition thereby made to the stock of human knowledge. 

 It is to this borderland lying between the well known and 

 the unknown, and to certain parts of the structure of the 

 eye having relation to it, that I would for a short time direct 

 your attention to-day. 



As I have already intimated, I propose to pass by en- 

 tirely the functions of the eye acting as a simple optical 

 instrument in forming images on the retina. The explana- 

 tion of that may be foiuid in all the ordinary text books, and 

 I will not weary you by repeating what is there to be found, 

 and whicli is generally familiarly known. 



The phenomena of vision show that distinctness of vision 

 is dependent somehow or other in the first instance on the 



