PROPERTIES OF LENSES. 



If an image of an object be received on a screen 

 placed opposite a small hole in the shutter of a dark- 

 ened room it will appear inverted, because the rays 

 from different points of the object cross at the aper- 

 ture. 



The size of the image varies inversely as the dis- 

 tance of the object, and directly as the distance of 

 the screen. 



If a convex lens be placed in the aperture, inverted 

 and diminished images of distant objects will be 

 formed on a screen placed at the principal focus. 



If an object (Fig. 4), be placed at twice the focal 



FIG. 4. 



distance of a convex lens, a real inverted image, the 

 same size as the object, will be formed on a screen 

 placed at a similar distance on the opposite side. 



If nearer, a real inverted magnified image (Fig. 5), 

 is formed at increasing distance until the principal 

 focus is reached, when no image is formed on the 

 screen, because the rays can never come to a focus 

 being parallel. 



FIG. 5. 



