Chap. 3.] Phenomena of concave Mirrors. 195 



unite at the point P. But if the point of divergence 

 was nearer the mirror than the principal focus, as for 

 inftance at K, they would ftill be reflected divergent* 

 and'would proceed one towards / and the other to- 

 wards b. 



Plane and convex mirrors exhibit, as -has been al- 

 ready mentioned, the image behind the glafs or mirror, 

 and in a fituation conformable. to that of the object; 

 but concave mirrors produce this effect only when the 

 object is. placed between the principal focus and the 

 mirror, and hen the image is larger than the -object. 

 Let AB (fig. 6.) be the object placed before the 

 concave mirror E F, and nearer to the mirror than 

 its principal focus. The two rays A <?, Rf> which pro * 

 ceed from the extremities of the object, and -which, 

 without the interpofition of the mirror, would converge 

 at d, are reflected more converging, and unite at > j 

 and making an. angle greater or more obtufe than they 

 would otherwife have done, the image a b is confe- 

 quently greater than the objtct. 



This image too appears 'at a greater diftance behind 

 the mirror than the object is at before it. The reafon 

 of this will appear, if we fuppofe A (Plate VII. fig. i.) 

 a point of any object placed nearer to the mirror than 

 the principal focus F, whence a pencil of divergent 

 rays proceeds, and falling on the mirror, are (accord- 

 cording to the principles before laid down) reflected 

 lefs divergent, and confequently have their virtual oi' 

 imaginary focus at a greater diftance than if the objedt 

 had been placed before a plain mirror. 



If, on the contrary, the object is placed farther from 

 the mirror than the principal focus, as for inftance at e, 

 the rays eb^ed y being only moderately divergent, when 

 they come in contact with the mirror, are reflected con- 

 vergent, and will represent at E an image of the ob- 

 O 2 ject, 



