VISION. 9 



covered, with one eye, some poppy seeds, which are 

 very small and inconspicuous*. 



In looking at objects which differ in their distances, 

 the eye has been supposed to undergo some change 

 of its parts or relations. It is supposed, in a word, 

 to do for itself what spectacles or glasses do for those 

 who are very long-sighted, or who are very near- 

 sighted. What this change is, has been the subject 

 of minute investigation and of learned discussion; 

 but still there is little with regard to it certainly 

 known. 



Sir Charles Bell is somewhat doubtful of the fact 

 of the alleged change in the eye, or, at least, he 

 thinks it much less than has been conjectured. He is 

 therefore inclined to ascribe what takes place, in look- 

 ing at near and distant objects, in a great measure 

 to attention. We can attend at pleasure to a letter 

 of a word, to the whole word, or to the page of a 

 book, in the same way as we can attend to a distant 

 object, while we overlook those which are nearly on 

 a line with it but nearer f. The mechanical effect 

 produced by thus directing the attention, Sir Charles 

 Bell does not attempt to trace. In a note, however, 

 on the iris, he states a fact of which he might have 

 taken advantage. When a cat is roused to attention, 

 as by the scratching of a mouse, the pupils of her 

 eyes dilate, ; and the same thing occurs when she 

 struggles to get loose from your hands }. 



Several ingenious experiments were made by Dr. 

 T. Young to discover the alleged changes in the 

 eyeball. He forced upon the ball of the eye the ring 

 of a key, so as to cause by its pressure a luminous 

 spot, and, looking at objects of different distance, he 



*Blicken en den Haushalt der Natur, p. 26, 1826. 



f Bell's Anat. Ft. ii. B. i. 11. vol iii. p. 334. 



I See also Fontana, Dei noti dell' Iride, ii. 17. 



