Professor Airy on a peculiar Defect in the Eye. 325 



face is turned from the eye. It alters the apparent figure of 

 objects by refracting differently the rays in different planes. 

 I judged it proper to have the frame of my spectacles made 

 so as to bring the glass pretty close to the eye. With these 

 precautions, I find that the eye which I once feared would 

 become quite useless can be used in almost every respect as 

 well as the other. 



Since I procured this lens, I have been informed that a 

 foreign artist has made spectacle-glasses with cylindrical sur- 

 faces of different radii for general use. What his object can 

 be I am quite unable to imagine. Certainly no one whose eye 

 is not defective can see with them distinctly. With my right 

 eye, which, (by the method of examination above described,) 

 I find to have no other defect than short-sightedness, I am 

 unable to read any thing in the lens made for my- left eye. 

 After many inquiries, I have not been able to discover that 

 this construction has been used to correct any defect in the 

 eye, or even that a defect similar to that which I have de- 

 scribed has ever been noticed. 



OBSERVATIONS BY THE EDITOR. 



We consider the preceding paper as a very interesting and 

 important one. The fact, we believe, has been before obser- 

 ved, that some eyes have a different refractive focus in a verti- 

 cal and in a horizontal plane, but we cannot at present refer Mr 

 Airy to the work which cohtains it. This, however, does not af- 

 fect the originality and value of his observations, of his successful 

 exertions to discover the nature of the defect, and to construct a 

 glass for correcting it. Mr Airy does not seem to have ascertain- 

 ed in what part of the eye this curious defect exists, — whether 

 in the cornea or in the crystalline lens. By examining the 

 image of a taper reflected from the outer surface of the cor- 

 nea, he will readily discover whether its form is spherical or 

 cylindrical. If it is spherical, there can be little doubt that 

 the crystalline is in fault, and it will remain to be determined 

 whether the differences of refraction in different planes arise 

 from the lens having one or both of its surfaces cylindrical, 

 or what is more probable, from a want of symmetry in the 

 variation of its density,- — an effect which is very common at 



