290 SENSE OF SIGHT. 



object will likewise appear extremely slow; hence the difference between 

 a carriage dashing past us in the street, and the same object viewed 

 from a lofty column. A balloon may be moving along at the rate of 

 nearly one hundred miles per hour; yet, except for its gradual diminu- 

 tion in size and intensity of light, it may appear to be at rest; and, 

 when bodies are extremely remote from us, however astonishing may be 

 their velocity, it can scarcely be detected. Thus, the moon revolves 

 round the earth at the rate of between thirty and forty miles a minute 

 above forty times swifter than the fleetest horse; yet her motion, during 

 any one moment, completely escapes detection ; and the remark applies 

 still more forcibly to those luminaries, which are at a yet greater dis- 

 tance from the earth. These are cases in which the body moves with 

 excessive velocity, yet the image on the eye is almost stationary; but 

 there are others in which the real motion is extremely slow and cannot 

 be at all observed; as that of the hour-hand of a clock or watch. 



It will be obvious, from all the remarks that have been made regard- 

 ing the information derived by the mind from the sense of sight, that 

 a strictly intellectual process has to be executed, without which no judg- 

 ment can be formed; and that nothing can be more erroneous than the 

 notion, at one time prevalent, that the method by which we judge of 

 distance, figure, &c., is instinctive or dependent upon an original "law 

 of the constitution," and totally independent of any knowledge gained 

 through the medium of the external senses. It has already been re- 

 marked, that metaphysicians may be considered as divided into those, 

 who believe that, without the sense of touch, the eye would be incapable 

 of forming any accurate judgment on these points ; and those who 

 think, that the sense of touch is no farther necessary than as an aux- 

 iliary, and that a correct appreciation may be formed by sight alone. 

 Messrs. Molyneux, 1 Berkeley, 2 Condillac, 3 &c., support the former view; 

 MM. Gall, 4 Adelon, 5 &c., the latter. 



Of the precise condition of the visual perception during early infancy, 

 we are of course entirely ignorant. So far as our own recollections 

 would carry us back, we have always been able to form a correct judg- 

 ment of magnitude, distance, and figure. Observation, however, of the 

 habitudes of infants would seem to show, that their appreciation of these 

 points especially of distance is singularly unprecise; but whether this 

 be owing to the sense not yet having received a sufficient degree of as- 

 sistance from touch, or from want of the necessary development in the 

 structure or functions of the eyeball or its accessory parts, we are pre- 

 cluded from judging. The only succedaneum is the information to be 

 obtained from those who have been blind from birth, and have been 

 restored to sight by a surgical operation, regarding their visual sensa- 

 tions. Although in the numerous operations of this kind, which have 

 been performed, it might seem, that cases must have frequently occurred 

 for examining into this question, such is not the fact; and metaphysi- 

 cians and physiologists have generally founded their observations on the 



1 Locke's Essay on the Human Understanding, book ii. chap. 9. 



2 Essay on Vision, 2d edit., Dublin, 1709. 3 Traite des Sensations, Part i. 

 Sur les Fonctions du Cerveau, i. 80, Paris, 1825. 



6 Physiologic de 1'Homme, edit, cit., i. 466. 



