422 THE OUTGO OF ENERGY 



larger than the object ; if at more than twic3 the 

 focal distance, the image will be smaller than the 

 object ; finally, if the object be situated between 

 the principal focus and the lens, the image will 

 no longer be real, but virtual and larger than the 

 object, as mentioned on page 419. 



BEFRACTION BY CONCAVE LENSES 



Place the diaphragm with 2 mm. aperture in 

 front of the condenser. Throw a pencil of paral- 

 lel rays into the box. Let the rays fall upon a 

 concave lens. 



The parallel rays will be rendered divergent. 



Look through the concave lens at printed 

 words. The image is virtual, upright, and 

 smaller than the object. It is nearer the lens 

 than the object, and is always within the prin- 

 cipal focal distance. 



KEFRACTION BY SEGMENTS OF CYLINDERS 



1. Place the diaphragm with 2 mm. aperture 

 in front of the condenser. Throw a pencil of 

 parallel rays into the box. Place the cylindrical 

 lens in the axis of the pencil in such a position 

 that the curvature shall be from side to side, i. e. 

 in the horizontal meridian. 



