184< Experimental Philosophy. [Lecture 13. 



has been described in the Philosophical Trans- 

 actions by Mr. Ware. 



The eye may be remedied when the crystalline 

 humour onJy is faulty ; but when there happens 

 to be a defect in the optic nerve, then the disorder 

 is almost always incurable. It is called the gutta 

 serena^ a disorder in which the eye is, to all ap- 

 pearance, as capable of seeing as in the sound 

 state ; but, notwithstanding, the person remains 

 for life in utter darkness. The nerve is insensible, 

 and scarcely any medical treatment can restore 

 its lost sensations. This is the disorder so 

 pathetically described by Milton in his lamenta- 

 tions on his own blindness. 



In the course of the preceding lectures it was 

 necessary to mention the angle of vision. But 

 you will now be able better to understand why 

 an object seen under a large angle, as near objects 

 are, appears larger than the same object would 

 at a distance. Thus men and women, when 

 you meet them in the street, appear of their na- 

 tural size, but if you look down upon them 

 from the top of St. Paul's, they appear as small 

 as puppets ; and thus if you look from one end 

 towards the other of a long and straight row of 

 trees, you will see them gradually diminish, as 

 they are further removed from your eye, though 

 on a near inspection you would find them all 

 of an equal size. The reason of this can be no 

 longer a secret. You are already informed, that 

 rays (or rather pencils of rays) are sent forth 



