DOUBLE REFLECTION OF GLASS MIRRORS. 435 



Common glass mirrors give rise to a double reflec- 

 tion ; for images are not only produced by the silvered 

 surface at the back, but also by the plane polished 

 front surface of the glass. The image produced by the 

 metallic surface possesses, however, a much greater 

 intensity of light than the reflection from the surface 

 of glass, and is usually alone observable ; but on holding 

 a burning candle, k in fig. 246, pretty close before a 



III! 



FIG. 246 (real size). 



common mirror, a distinct image, a, is seen to be reflected 

 by the silvered surface, and a more feeble one, b, is re- 

 flected from the glass surface of the mirror; but besides 

 these there are several other reflected images seen, 

 whose intensities gradually decrease. These images 

 arise from the repeated reflections which take place 

 between the two surfaces. 



A piece of unsilvered plate -glass produces not only 

 a reflected image of an object placed in front of it, but 

 also allows light to pass through it from objects behind 

 it. It may thus be arranged that two objects appear 



F F 2 



