Stoney— Limitation of Insect Vision. 235 
afterwards to another. If we repeatedly seize opportunities of 
making this experiment we shall gradually accumulate instances 
of every degree of vividness, from the full distinctness of a dream 
in respect of colour, brightness, and form, down to the shadowy 
dimness of what we very imperfectly see in the exercise of ordinary 
memory. ‘The same important observation may be made here, as 
on a former occasion. The objects so seen do not shift their posi- 
tions when we voluntarily shift 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. 
Another 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 thoughts. 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 towards which our eyes. 
may chance at the time to be directed, becomes less distinct, and, in 
extreme cases, may almost fade out, so that even noteworthy events 
may happen in our presence which we do not see, or at least, which 
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 ona 
tricycle—on an unusually dark night in summer from Glendalough 
to Rathdrum. It was drizzling rain, we had no lamps, and the 
road was overshadowed by trees on both sides, between which we 
could just see the sky-line. Iwas 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 bit of tin or some- 
thing else in the road that made a great crash. Presently my com- 
panion 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 standpoint] evoked the other, 
