REFRACTION BY CONVEX LENSES. 



being at the centre, there is no convergence at all, the rays being 

 merely rendered parallel (Fig. 3) ; whilst, if the point of divergence 

 be beyond the diameter of the sphere of curvature, the point of 

 convergence will be within it (Fig. 5). The farther removed the 

 point of divergence, the more nearly will the rays approach the 



Fig. 5. 



Rays diverging from points more distant than the principal 

 focus of a double-convex Lens on either side, brought to a focus 

 beyond it ; if the point of divergence be within the diameter of 

 curvature, the focus of convergence will be beyond it ; and vice 

 versa. 



parallel direction : until, at length, when the object is very dis- 

 tant, its rays in effect become parallel, and are brought together 

 in the principal focus (Fig. 3). If, on the other hand, the point 

 of divergence be tvithin the principal focus, they will neither be 



Fig. 6. 



Rays already converging, brought together by a double-convex 

 Lens at a point nearerthan its principal focus ; andtays diverging 

 from a point within its principal focus, still divergent, though in 

 a diminished degree. 



brought to converge nor be rendered parallel, but will diverge in a 

 diminished degree (Fig. 6.) And conversely, if rays already con- 



