THE PERCEPTION OF LIGHT. 



The Report that has just been read shows that the Institute 

 fully maintains the position it occupied at our last Anni- 

 versary Meeting — might I not even say that it indicates 

 a general and increasing interest ? The utility of the 

 Institute depends, in my opinion, very largely on the 

 maintenance of an impartial, truth-loving spirit in the in- 

 vestigation of questions on which the conclusions to which 

 we appear to be led by observation and experiment, and 

 those which seem to us to be inferences from what we 

 believe to have been communicated to man in a wholly 

 different manner, are both involved. 



I regret that the Anniversary Meeting of the Victoria 

 Institute had to be postponed this year to a date later than 

 usual, which I fear may be less convenient to some of our 

 Members, because unforeseen circumstances prevented us 

 from having an important paper which we had intended to 

 bring forward at the Anniversary. In default of that 

 paper, I propose to invite your attention for a short time 

 to a subject of great interest, though I am sorry to say it 

 lies in great measure outside the line of my own re- 

 searches. 



At a former Anniversary I brought before the Members 

 of the Institute the subject of the Luminiferous Ether. It 

 is one of great and growing interest. I mentioned on that 

 occasion how discoveries of very recent date have led us to 

 attribute continually increasing importance, and a widening 

 range of function, to that medium — substance can I call 

 it? — the existence of which was originally assumed as a 

 hypothesis in order to account for the phenomena of light. 

 It is in connection with this last aspect that it relates to 

 what I propose to bring before you to-day. 



The wonderful sense of sight, which, to use an expression 

 of Sir John Herschel's, confers upon us to some extent the 

 character of ubiquity, requires two things : in the first place, 

 some means by which those distant bodies which we see are 



