Reflexibility of Light. 1 75 



proved by drawing the dotted lines C A, Cc, CB, 

 from the centre of concavity to the points whence 

 these rays are reflected, which are therefore per- 

 pendiculars to the surface of the mirror. The 

 angle C Ad, or the angle of reflection, you see, is 

 equal to DAC, the angle of incidence, and so 

 you will find it of the rest. The reflected rays 

 then, you see, converge to a point, and form the 

 extremity of the dart (which is now inverted) 

 at d. In the same manner every other pencil of 

 rays emitted from the object, will be converged 

 at or near the principal focus, and the image will 

 be formed at e d. For you wih 1 perceive that if 

 the rays E t /J T5g*, ' E A, were continued to the 

 mirror, they would be reflected and converged at 

 e^ forming the opposite extremity of the dart. 

 When the object is further from the mirror than 

 the centre of concavity C, the image wih 1 be 

 nearer the mirror, and smaller than the object; 

 when the object is nearer than the centre of con- 

 cavity, the image will then be more remote, and 

 larger. Thus, if e d was the object, DE would 

 be the reflected image. 



It is not many years since a person derived 

 considerable emolument from exhibiting in the 

 metropolis some optical deceptions of this kind, 

 with concave mirrors. A ghastly apparition was 

 sometimes made to meet the ignorant spectator, 

 and from its shadowy appearance it was evidently 

 nothing human ; sometimes a hand was held out 

 in the air, with every possible mark of friendship, 



