80 



PRACTICAL LESSONS IN SCIENCE. 



the double concave lens is to render rays parallel to the principal 

 axis divergent. 



Experiments with diverging and converging rays show that 

 the general effect of the double concave lens is to disperse rays of 



FIG 14 



light. Experiments with the other concave lenses show the same 

 effect. 



The double convex lens, or any of the convex lenses, not only 

 collect rays of light, but rays of heat as well, and are sometimes 

 called burning glasses. These lenses are also used as magnifying 

 glasses, or simple microscopes. The relations of images to ob- 

 jects in different cases are shown in the following figures (see 

 Fig. 15), in which the object is between the focus and the lens. 



Let MN represent the lens whose focus is at C, and let the ob- 

 ject AB be placed between 



s' 



Fic.15. 



point and the lens ; if we 

 trace the rays of light from 

 the object through the lens, 

 they are diverging after re- 

 fraction and cannot meet; 



but if the eye receives these rays at E, they will have the same 

 effect as if they came from A' and B' ; hence the image will be 

 formed at A'B', which will be on the same side of the lens as 

 the object, erect and larger, than the object. In case the object 



