113 On Opl'u Fis'tott, 



eve, stripped behind of its sclerotica and choroid inem'jraiie. 

 The retina being con«idered a propasxation of the substance of 

 the optic nerve, its claims as the true seat of vision were never 

 questioned till Marriotte, from his investigations into the struc- 

 ture of the organ, and optical experiments, rejected theni in fa-^ 

 vour of the choroides. Hence the famous controversy com- 

 menced betv/een him and Pecquet, who vindicated the rights 

 of the retina against his hypothesis. The experiments and ar- 

 guments were so balanced, that scientific men were for a time 

 divided in their opinions. The hypothesis of Marriotte, how- 

 ever, at length fell into disrepute, and the general opinion ever 

 since lias been, that the retina is the proper seat of vision. 



However, after a careful examination of the various parts of 

 the organ, and close investiii;ation of the phjenomena attending 

 various and repeated experiments, I have been induced to assign 

 the chief function in vision to tiie base of the optic nerve, and to 

 conclude tliat the optic images are formed bv caustic reflection, 

 and exhii)ited in the middle of the Titreous humour; and thus 

 the optic impression and position of the tangible object are re- 

 conciled*. Among a variety of reasons and experiments, I have 

 adduced the well known experiments of Daniel Bernoulli and 

 Le Cat, but ef^pecially the famous experiment of Marriotte made 

 with the patches upon the wall, as confirming the theory almost 

 beyond the shadow of a doubt. Since the publication of my 

 work, I have understood that some have questioned the truth of 

 the theory! As a further confirmation of it, I made the follow- 

 ing experiments upon Marriotte's principles. I fixed three cir- 

 cular white papers, at the height of my eye, upon a wall of a 

 j:a!e green colour; the middle one was ten inches in diame- 

 ter; the two otliers were each about two inches in diameter, 

 and placed at two feet from the centre of the middle paper. 

 On retiring with my right eye closed, and the left eye directed 

 to the paper on the right hand, v.hen at the distance of nearly 

 four feet from the wall, tfie obscurity of the middle object wa-^ 

 first indicated by the disc becoming invisible except a small 

 white ring; but iVoni the unsteadiness of the eye in its distorted 

 state, I found it very difficult to make the ring appear perfectly 

 annular; its sphericity would now be seen interrupted in the 

 upper part, in an instant it would change to the lower part, and 

 in the next instant the interruption would be on one side or the 

 other. When I had retired about three inches further, I lest 

 the object entirely; and the whole wall between the two extreme 



* Sec a small Treatise published by lue, " The Seat of Vision deter- 

 mined bj- tlic Discovery of a nc%v Function in the Organ ;" or the last editioa 

 of Dr. Ilutton's I'iiiloijoph. and Mathcmat. Dictionary, article Vision. 



object'?, 



