320 ON LIFE AND ORGANISATION. 



the retina, on the greater visual delicacy of the central retinal spot, 

 on the relative position of the two eyes, and on the muscular sense ; 

 and, physiologically, on the faculties of attention, memory, and 

 conception under the conditions of thinking in space. 



The mosaic structure of the retina permitting only the sensation 

 and perception of a single point of light for each compartment of 

 its surface, must necessarily afford the immediate means of con- 

 ception of breadth, or of transverse and perpendicular separation, 

 under the condition of thinking in space. The mosaic structure of 

 the retina will thus at once, and without any movement of the eye 

 or head, afford to the infant the means of judging of the separation 

 of two points of light in the field of vision. 



But much more extended and precise conceptions of the rela- 

 tions of breadth, or of transverse and perpendicular separation, 

 are acquired through the muscular sense in the movements of the 

 eyeball and head. These movements may be stated, generally, to 

 have as one of their more important objects the bringing of the - 

 central or most delicate part of the retina opposite to each part of 

 an object in succession. These successive movements constitute, 

 in fact, a process of palpitation, during which the central spot, or 

 most delicate part of the eye — considered as an organ of touch — in 

 combination with the muscular sense, is successively brought into 

 contact with the object examined. Through its faculties of atten- 

 tion, memory, and conception, under the conditions of thinking in 

 Space, the mind stores up, and retains, in their proper relative posi- 

 tions, the successive perceptions it has acquired by the successive 

 mediate applications of the central spot to different points of the ob- 

 ject looked at, and in this manner is enabled to piece them together, so 

 as to frame a conception of the object as a picture — that is, as consist- 

 ing of parts, all situated in a plane transverse to the axis of the eye. 



The self-consciousness of the infant now acquires the faculty of 

 detaching its visual conception of an object from its eye. It has 

 hitherto seen it as a picture in a transverse plane, and at the eye. 

 It has now to see it — that is, to conceive of it through visual per- 

 ceptions — as a solid object (if it should be a solid object) in its pro- 

 per position in relation to other objects in Space. 



Two means conduce towards this end : the position of the two 

 eyes, and the exercise of the muscular sense. 



