BY THE PRESIDENT. 
125 
seen things in their proper position. Chickens which have been 
blindfolded immediately after leaving the egg have, on removal 
of the hood, pecked at grain with the unerring aim of an old bird.* 
The most probable theory appears to be, that there is a complex 
relation between the position of the eye and that of the image 
on the retina, and that both are factors leading to a correct judg¬ 
ment which depends upon complex relations between different 
parts of the brain. 
We have also obtained a very different idea of the size of 
external objects as compared with their image on our small retina. 
The perceptions of distance and size which we derive solely from 
our field of vision are limited to the relative size and position of 
the different objects in the field, and this alone would be of little 
service to us. We learn from the sense of sight the topographical 
relations of objects, but it is the sense of touch and muscular 
movement which has enabled us to judge of size, and it is the 
association of the two senses which has formed our interpretation 
of the size and distance of objects in the image thrown on our 
retina. If we hold, say, an envelope in one hand, and pass the 
other round its form, we have an idea how in infancy we first 
obtained a judgment of the size of an object which we saw. 
The relative size of known objects in the field of vision to un¬ 
known ones enables us to form judgments of the latter. But the 
perception of the size of an object varies with concurrent condi¬ 
tions. Thus the moon appears smaller at the zenith than on the 
horizon, for we are then influenced by its relative size to terrestrial 
objects. Again, just as we are deceived as to distance by the 
muffled voice of the ventriloquist, so are we by the size of a man 
whom we see in a fog. The indistinctness of the image gives us an 
idea of distance, for which we make an allowance, and thus think 
the man larger than he is. ISTor does an object appear to be of the 
same size to every individual. The image of the full moon on the 
retina of all human beings is about -rib-th part of an inch in dia¬ 
meter, yet few will agree as to its apparent size. Our perception 
of magnitude is widely different from what it was in our child¬ 
hood, and there is every reason to believe that the apparent size of 
any object varies throughout the animal kingdom according to the 
structure of the organism. In truth all our notions of size and 
position and solidity are visual judgments and depend as much on 
the brain as on the eye. The further consideration of these matters 
would carry us far beyond the limits of my address. 
* See Spalding’s experiments in ‘ Macmillan’s Magazine,’ Feb. 1873. 
