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THE POPULAR SCIENCE MONTHLY 



is exclusively the result of a change in the eyes, which developed 

 itself during the last twenty years of his life. In consequence of 

 it, the aspect of Nature gradually changed for him, while he con- 



Fio. 1. 



tinued in an unconscious, I might almost say in a na'ive, manner 

 to reproduce what he saw. . . ." 



That astigmatism distorts objects can be easily demonstrated. 

 It is well known that the structure of the human eye is practi- 

 cally the same as that of the photographer's camera. Ordinarily 

 the image which falls on the glass plate of the camera is equally 

 clear in every part, because the lenses in front are ground with 

 spherical surfaces. Such a camera when properly directed at 

 a picture like that of the Taj Mahal, for example, gives us on 

 the glass plate a clear and undistorted image of the building, 

 such as is seen in Fig. 1. If, now, we render the front glass of 

 the camera slightly astigmatic, by placing in front of it a so- 

 called cylindrical glass with the axis horizontal, it produces 

 optically exactly the same effect as that obtained when the globe 

 of the eye is pressed from above downward. Moreover, the de- 

 gree of this distortion in any eye can be reproduced with perfect 

 exactness by placing in front of the camera a cylindrical glass 

 of proper strength. It will be remembered that the average de- 

 gree of astigmatism with the artist's examined was found to be 



