with Special Reference to the Vision of Insects. 323 



former occasion. The objects so seen do not shift their 

 positions when we voluntarily move our eyes about. They 

 have their origin not in the retina, but in immediate connexion 

 with the part of our brain which is directly related to our 

 judgments about space. 



Ar other interesting observation is of what happens when 

 we get into what is sometimes called a " brown study " — 

 thinking intently upon some past scene that engrosses our 

 attention. On such occasions the visual image before " our 

 mind's eye " becomes more vivid than usual, and in the same 

 degree the image produced in the ordinary way of the external 

 objects tovards which our eyes may chance at the time to be 

 directed becomes less distinct, and, in extreme cases, may 

 alnrost fade out, so that even noteworthy events may happen 

 in our presence which we do not see, or at least wnich do not 

 impress us sufficiently for us to retain any memory of them. 



Two experiences, one of a friend and one of myself, seem 

 worth recording in this connexion : — 



Some years ago this friend and I rode — he on a bicycle, I 

 on a tricycle — on an unusually dark night in summer from 

 Glendalough to Rathdrum. It was drizzling rain, we had no 

 lamp:, and the road was overshadowed by trees on both sides, 

 between which we could just see the sky-line. I was riding 

 slowly and carefully some ten or twenty yards in advance, 

 guiding myself by the sky-line, when my machine chanced 

 to pass over a piece of tin or something else in the road that 

 made a great crash. Presently my companion came up, 

 calling to me in great concern. He had seen through the 

 gloom my machine upset and me flung from it. The crash 

 had excited the thought of the most likely cause for it, and 

 the event in his brain, which was the physical adjunct of the 

 thoughts thus passing through his mind, were so associated with 

 that other event in the brain, which is the adjunct of visual 

 consciousness, that the one (speaking from the physical stand- 

 point) evoked the other, perhaps faintly. This involved a 

 visual perception in the mind faint, but sufficient on this 

 occasion to be seen with sufficient distinctness when not over- 

 powered by objects seen in the ordinary way through the 

 eyes. 



The experience I had myself was one which frequently 

 occurred to me when a lad. Several of us boys were fond of 

 witnessing sham fights in the Phoenix Park, at which some of 

 the most conspicuous objects were the single horsemen who 

 now and then galloped at full speed, with orders, from one 

 part of the field to another. Almost always, after a day spent 

 in viewing this spectacle, as I lay in bed at night I saw 



