381* 



power of my eyes for horizontal and for vertical rays, and to 

 determine whether they possess a power of adjustment for 

 different distances." By T. WHARTON JONES, Esq., F.R.S., 

 Professor of Ophthalmic Surgery in University College, 

 London, &c. Received March 8, 1860. 



Besides the well-known differences of sight in respect to farness 

 and nearness, there are differences in respect to the power of the 

 eyes of different persons to bring the rays of light to one exact focus. 



From observations and experiments in which I have for some time 

 been engaged, I have been led to suspect that astigmatism or inca- 

 pacity of the eye to collect all the rays of light which enter it to 

 one exact focus, is, if not the rule of sight, at least of very common 

 occurrence. I do not here refer to the cases in which astigmatism is 

 of so exaggerated a character as to be a positive defect of sight. 



It would be of great importance, both in a scientific and practical 

 point of view, to possess some accurate data as to the frequency of 

 the occurrence of astigmatism ; but such can be obtained only by a 

 number of different persons qualified observers contributing each 

 an analysis of his own sight. I have thought, therefore, that by 

 bringing under the notice of the Royal Society an analysis of my own 

 sight, some of the Fellows and others accustomed to exact observations 

 might, perhaps, be induced to make similar contributions. The 

 adjustment of the eyes for different distances being intimately con- 

 nected with the question of stigmatism or astigmatism, I have included 

 it in my analysis. 



If I view a vertical and 

 horizontal line, both equally 

 strong and black, I see them 

 with medium distinctness at 

 the distance of about 10 

 inches. 



At the distance of about 

 8^ inches, I see the vertical 

 line with greater distinctness 

 and better definition the 

 greatest distinctness and best 

 definition my eyes are ca- 



* Continued from page 3/4. 



