662 DEMONSTRATING REFRACTIVE EYE DEFECTS [Cn. XV 



90 



,06 



FIG. 389. THE RADIAL LINES SHOWING THE SIZE OF THE IMAGE WITHOUT 

 SPECTACLES, AND WITH CONCAVE AND CONVEX SPECTACLES. 



A shows the size of the image without spectacles. 



B shows the diminished size of the image when a spectacle lens of .5 diopter 

 is put with the 5.5 diopter lens. (This reduces the 5.5 to a 5 diopter lens). 



C shows the increased size of the image when a spectacle lens of +.5 diopter 

 is added to the 5.5 diopter lens. (This increases the 5.5 diopter lens to 6 

 diopters). 



The photographs were made by fixing the camera so that the objective and 

 sensitive plate were at a constant distance, then the image was focused by 

 moving the object farther off for B and nearer to the lens for C, just as in the 

 projection experiments ( 922). 



