LIGHT. 83 



four times as much light as it did at /. Hence the in- 

 tensity of light varies inversely as the square of the 

 distance. Other measures with other distances can be 

 made for confirmation : a good exercise for scholars. 



Fig. 62. 



When a lantern must be used in place of sunlight, it 

 will be necessary to remove the objective and move the 

 light backward from the condenser until a sharp focus 

 is produced in front, and then work in front of that ; or 

 still better, remove both condenser and objective, the 

 outlines of shadows will be quite well defined with the 

 electric light, and with the lime light, but not with any 

 oil light. 



REFLECTION. 



The reflecting power of various surfaces can be 

 shown by holding them in the path of the beam from 

 the reflector. Common mirrors, plain glass, colored 

 glass, metals polished and unpolished, woods, horn, 

 polished stones, paper, will all exhibit difference in this 

 property. 



Reflection from the two surfaces of glass is seen 

 upon the screen when the parallel rays from the first 

 mirror reach it. Then will always be seen two or 

 three indistinct images of the sun, side by side. When 



