ORGANS OF PERCEPTION. 193 
which no habit or experience during their limited existence 
could reduce. I have observed, that children, from the 
time that they are capable of fixing their eyes steadily on 
any object, direct both of them towards it; and this effort 
they do not seem capable of making, until the iris has ac- 
quired the power of dilating and contracting. 
3. KNOWLEDGE OBTAINED BY THE SENSE OF SIGHT.— 
The information communicated to the mind by means of 
the sense of sight, is, perhaps, more varied than that of 
touch, but it is less accurate. The qualities and conditions 
of objects primarily ascertained by this sense, may be re- 
stricted to colour and direction merely. It is true, that we 
rely on the information which it. communicates with regard 
to the distance, form, size and condition of the surface of 
bodies ; but in these cases we are apt to be deceived, unless 
aided by the recollections of the sense of touch. 
The eye is the only organ of the body, which is fitted to 
examine the quantity, quality, and motions of the rays of 
light. Hence we owe to it all our ideas with respect to 
the colour of bodies. We readily perceive the limits of dif- 
ferent coloured spaces, and thereby ascertain their shapes 
and degree of illumination. Aided by the experience and 
the sense of touch, we speedily judge of the boundaries of 
objects themselves, by the distribution of colours, and their 
distance by their brilliancy. But in order to preserve the 
eye in a condition capable of perceiving correctly the diffe- 
rences among bodies with respect to colour, it is necessary 
that it be prevented from looking long on any one colour at 
a time, least the retina become fatigued, and less easily ex- 
cited to receive impression. When the retina is thus fa- 
tigued, the eye ceases to judge accurately with regard to 
colour, seeing those only which have been termed accidental. 
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