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ON THE INFLUENCE OF THE 'SENSE' OF MUSCULAR 

 ACTION IN CONNEXION WITH VISION. 

 BY ALEXANDER SHAW, ESQ. 



^PO those philosophers who have studied the subject of 

 sensation, the organ of vision has ever been the most 

 attractive ; and yet the opinions of men, whose attainments 

 we must respect, differ very widely as to the mode of opera- 

 tion of this external organ of sense. 



Dr. Brewster, in his Treatise on Optics,' which is the 

 latest publication on this subject, has introduced an explana- 

 tion of the problem Why an inverted image on the retina 

 should give us the idea of an erect object. This question, as 

 he himself has remarked, has been a frequent cause of per- 

 plexity to the learned ; but I am of opinion that no theory of 

 vision can be admitted to be correct, which does not afford a 

 satisfactory explanation of it. 



This problem involves certain physiological principles, 

 which are not generally understood, but upon which the doc- 

 trines of perception through the organs of the senses, espe- 

 cially the eye, have the most intimate dependence. As the 

 solution, which Dr. Brewster has adopted, is unconnected, 

 and, indeed, altogether at variance with these, it becomes ne- 

 cessary to examine it with care ; and I think it can be shown, 

 notwithstanding the confident tone in which he has expressed 

 himself, and the high authority which he deservedly holds in 

 questions of optics, that the explanation which he has offered 

 is liable to many powerful objections. It is the more im- 

 portant to undertake this examination, since the view which 

 he has presented may be considered as that which generally 

 prevails. It is the same explanation which was originally pro- 

 posed by Dr. Porterfield in the ' Medical Essays,' and Dr. 

 Reid, when treating of the mode of operation of the organ of 

 vision in his ' Inquiry into the Human Mind,' has explained 

 it upon the same grounds. 



These writers have all agreed in representing that the idea 

 of the ' direction ' in which objects are seen is obtained imme- 

 diately from the retina or nerve of vision. They suppose that 

 this nerve can convey to the mind a sensation of the course in 



