472 



REFRACTION THROUGH LENSES. 



If the distance of the object from the lens is greater 

 than twice the focal length, as in fig. 271, the image is 



FIG. 271. 



smaller ; if the distance is less, as in fig. 272, the 

 image is greater than the object. In both cases the 



FIG. 272. 



contraction which leads to the determination of the 

 position of the images is quite similar to that explained 

 with reference to fig. 270, and the same letters are 

 employed in all three figures for corresponding points. 



FIG. 273. 



Let, in fig. 273, the object AB be between the lens 

 and its principal focus, the latter being denoted by c for 



