LIGHT. 



CONCAVE MIRRORS. 



rig. 67. 



Concave mirrors, sufficiently good for demonstration, 

 are fitted to wall lamps, or the reflector generally fitted 

 to oil lanterns may be used. Such a one held in the 

 path of the beam from the porte lumiere will reflect 

 the rays to a focus, where there will be sufficient heat 

 to ignite wood, paper, etc. If the mirror be tipped, 

 the beam, after passing the focus, will diverge and 

 cover the whole ceiling, as the focus is quite close 

 to the mirror. 



Fig. 68. 



The image formed in front of the concave mirror 

 may be seen by letting a strong light fall upon the 

 object and having the mirror above it, as indicated. 

 If the object o be inverted and hidden otherwise from 

 view, it will appear upright ; and at d , to one standing 

 in front of the mirror, all in a room can be made to 

 see it by turning the mirror a little, so it will face them. 



