82 PHILOSOPHICAL TKANSACTIONS. [ANNO 1797- 



first she was unable to see at all with the imperfect eye, but in some weeks she has 

 improved so much as to be able to work at her needle with it; this she cannot do 

 long at any one time, the eye being soon fatigued and requiring rest, though with- 

 out giving pain. She is unable to read with the imperfect eye. These trials have 

 only been made in the course of 2 months, for a few hours in the day, and her 

 friends think that she squints less frequently than she did. In this case it is pro- 

 bable that the imperfect eye never had acquired the power of adjustment to near 

 objects; for as distinct vision seems necessary to direct the muscles in their actions, 

 the perfect eye would require less practice to adjust itself than the other; and as 

 soon as the near object became distinct to one eye, no information being conveyed 

 to the mind of the failure in the other, all efforts to render its adjustment perfect 

 would be at an end, and it would ever after be neglected, while the perfect eye was 

 in use. 



Squinting, according to these observations, appears to arise from the vision in 

 one eye being obscure. It may however be acquired in a degree by children who 

 have the lenses of their eyes of different focuses; or have one eye less perfect in its 

 vision than the other, living constantly with those who do squint, and by imitation 

 acquiring a habit of neglecting to use one eye. The power of squinting volunta- 

 rily may also be acquired at any age. This we find to be true in persons who look 

 much through telescopes; they are led to apply the mind entirely to one eye, not 

 seeing at all with the other. In this case the neglected eye will at first, from habit, 

 follow the other; but in time, if frequently neglected, may lose this restraint, 

 and be moved in another direction. Some astronomers, whose eyes have been 

 much used in this way, are said to be able to squint at pleasure. 



From this view of squinting, it takes place under the 3 following circumstances: 

 where one eye has only an indistinct vision ; where both eyes are capable of seeing 

 objects, but the one less perfect in itself than the other; and where the muscles 

 of one eye have acquired from practice a power of moving it independently of the 

 other. When squinting arises from an absolute imperfection in the eye, there can 

 be no cure. Where it arises from weakness only in the sight of one eye, it may 

 in some instances be got the better of; but to effect the cure there is only one 

 mode, which is that of confining the person to the use of the v/eak eye by covering 

 the other; in this way the muscles, from constant use, will become perfect in the 

 habit of directing the eye on the object, gain strength in that action, and acquire 

 a power of adjusting the eye; when these are established in a sufficient degree, the 

 other eye may be set at liberty. The time that will be necessary for the cure must 

 depend on the degree of weakness of the sight, and the length of time the mus- 

 cles have been left to themselves; for it is with difficulty they acquire an increased 

 degree of action, after having been long habituated to a more limited contraction. 



On the nature of the cornea, some of its diseases, and mode of treatment. — The 

 cornea of the eye, as the name implies, has been considered of a cuticular nature. 

 Haller compares it to the nails in a soft state, and believes that in its regeneration 



