410 THE OUTGO OF ENERGY 



will be reflected through the principal focus. 

 Draw a second incident ray from the arrow point 

 through the centre of curvature. This ray will 

 be perpendicular to the spherical surface and 

 will be reflected in the same line. The inter- 

 section of these two reflected rays will be the 

 image of the point of the arrow. 



Determine in like manner the position of the 

 image of the other end of the arrow. 



KEFLECTION FROM CONVEX MIRRORS 



The laws of reflection from 'convex mirrors 

 may be deduced from those already stated for 

 concave mirrors. The image reflected from con- 

 vex mirrors is virtual, upright, and smaller than 

 the object. 



Determine by construction the length of the 

 image of an arrow, 2 cm. long, placed 10 cm. 

 from the middle point of a convex mirror of 

 5 cm. radius. 



EEFRACTION 



1. Place the diaphragm of 2 mm. aperture in 

 front of the condenser. Push in the draw-tube of 

 the lantern until a beam of parallel rays enter 

 the box. In the box lay' the square glass bottle 

 on its side upon a wooden block and at right 



