802 



WELLS'S NATURAL PHILOSOPHY. 



t ff 1 1 "^^^ atmosphere reflects light irregularly, and every particle 



the atmosphere of air is a luminous center, which radiates light in every direc- 



upon the diffu- tj^Q^ -^g^g j^ not for this, the sun's light would only illumi- 

 Bion of light? ' ° •' 



nate those spaces which are directly accessible to its rays, and 



darkness would instantly succeed the disappearance of the sun below the horizon, 



05Q. Any surface which possesses the power 

 of reflecting light in the highest degree is called 



"What is 

 Mirror ? 



a Mirror. 



Into how many 

 ' classes are mir- 

 rors divided ? 



Mirrors are divided into three general classes, 

 without regard to the material of which they con- 

 sist, viz.. Plane, Concave, and Convex Mirrors. 



These three varieties of mirrors are represented in Fig. 

 233; A, being plane, like an ordinary' looking-glass; B, 

 concave, like the inside of a watch-glass ; and C, convex, 

 like the outside of a watch-glass. 



AVhat is the 657. Whcu light falls upon 

 fi^r'rcfle'ction » plane and polished surface, 

 ©flight? ^]jQ angle of reflection is equal 



to the angle of incidence. 



This is the great general law which governs the reflec- 

 tion of light, and is the same as that which governs the 

 motion of elastic bodies. " 



Thus, in Fig. 234, let A B be the direction of an inci- 

 dent ray of light, falling on a mirror, F C. 

 It will be reflected in the direction B E. 

 If we draw a line, D B, perpendicular to 

 the surface of the mirror, at the point of 

 reflection, B, it will be found that the 

 angle of incidence, A B D, is precisely 

 equal to the angle of reflection, E B D. 



The same law holds good in 

 regard to every form of surface, curved as well as plane, 



since a curve may be supposed 

 to be formed of an infinite num- 

 ber of little planes. 



Thus, in Fig. 235, the incident ray, E 0, 

 falling upon the concave surface, a C b, 

 will still be reflected, in obedience to the 

 same law, in the direction C D, the angle 

 being reckoned from the perpendicular to 

 that point of the curve where the incident 

 ray falls. The Bame will also be true of 

 the convex surface, A G B. 



