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 ray? 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 die diffe- 

 rences ai n^ig 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. 

 VOL. i. N 



