104 EXPERIMENTS, &c. 



them, the optic axes penetrate the glasses more 

 inwardly than their centres. But I can be by 

 no means sure, that the interval of the pupils 

 of other persons, bears the same proportion to 

 the interval of the centres of the lenses in spec- 

 tacles, as that of mine does. It concerns those, 

 therefore, who are choosing them, to have at- 

 tention to this circumstance. To me it appears 

 proper, that the glasses in spectacles, both for 

 long and short-sighted people, should be so far 

 asunder, that, when we look at a very remote 

 object directly before us, our optic axes may 

 pass exactly through their centres. For if the 

 centres of convex glasses be nearer to each 

 other, very remote objects will appear double ; 

 and if they are more distant, though the object 

 viewed be infinitely far from us, the optic axes 

 will, however, be inclined to one another, and 

 the refractive power of the eyes increased, 

 when this may be of disservice ; since there 

 are few eyes which are not able, even without 

 the aid of the convexity of a glass, to bring 

 parallel rays to a focus upon the retina. If the 

 centres of lenses in spectacles, for the short- 

 sighted, be less distant than what I have men- 

 tioned, the optic axes must be bent toward 

 each other, when very remote objects are seen, 

 and the refractive state of the eye, therefore, 

 heightened, which is the very reverse of whaj: 



