Ref i eligibility of Light. 155 



to a point or focus; the rays of the sun, how- 

 ever, come from so great a distance, that they 

 are always regarded as parallel. Divergent rays, 

 such as proceed from a point, as the flame of a 

 candle, will be refracted parallel. If, therefore, 

 we place a candle exactly at a focal distance from 

 one or both of these glasses, as at^J its rays will, 

 upon going through the glass, all run parallel to 

 each other. If the candle is placed nearer the 

 glass than its focal distance, the rays, after passing 

 through the glass, will no longer run parallel, but 

 separate or diverge : if it is placed farther off, 

 the rays will then strike the glass more parallel, 

 and will therefore, upon passing through it, con- 

 verge or unite at some distance behind the glass. 

 After the rays have united or converged to a 

 focus, they will cross each other, and form an 

 inverted picture of the flame of the candle, as 

 may be seen on a paper placed, at the meeting 

 of the rays behind. How the image is inverted, 

 therefore, is easy to apprehend ; for the upper 

 rays, after refraction, were such as came from 

 the under part of the luminous body ; and the 

 under rays, on the contrary, came from its top : . 

 so that the rays are turned upside-down, and So 

 consequently is the image. It is very pleasing 

 to view a picture of this kind thus formed, each 

 ray preserving the colour it had in the luminous 

 object with the utmost imitative precision. The 

 shadings of the little piece are far beyond the 

 reach of art, and the design far more correct 



