SPHERICAL EEFLECTOES. 



those through which the object is moved. In fine, when the 

 object approaches to F, the image will recede indefinitely behind 

 the reflector, and will disappear altogether when the object 

 actually arrives at F. 



All these phenomena admit of easy verification, by placing a 

 candle in the several positions here assigned, and observing its 

 image reflected in the mirror. 



13. If the reflector be convex, the object L M (fig. 8), will have 



points I m, between the reflector and the 



its image at the 

 principal focus F. 



The rays pro- 

 ceeding from the 

 several points of 

 the object L M 

 will, after re- 

 flection, diverge 

 as if they had 

 proceeded from 



the corresponding points of I m, and will produce upon the vision 

 the same effects as if an object had been actually placed at I m. 



The image in this case, therefore, will be erect, and it will 

 be less than the object in the proportion of o I to o L. In this 

 manner is explained the effect familiar to every one, that convex 

 reflectors exhibit a diminished picture of the object placed before 

 them. 



14. IMAGES PRODUCED BY TRANSPARENT BODIES. 



When light enters or issues from'a transparent body its direction 

 is deranged, its rays appearing to be broken at the points where 



Fig. 9. 



they pass through the surface of 

 the body. This effect is called 

 refraction. 



15. Thus, if the line A B (fig. 

 9) be supposed to represent the 

 surface of such a body, and that 

 a ray, E i, enter it at i, this ray, 

 instead of preserving its direc- 

 tion, will be broken, as it were 

 at i, and will take the direction 

 i R. If the ray has been transmitted from R to i, it would, on 

 issuing from the surface A B at i, have been broken, and would 

 take the direction I E. 



Let the line N N' be drawn perpendicularly to the surface A B. 

 If the ray E i be supposed to enter the surface at I, it will be 

 always refracted towards the perpendicular I N'. 



89 



