53 



If nine candles are used instead of four, where must D 

 be placed to produce the same illumination as one candle 

 alC? 



State the law regarding the intensity of light at any dis- 

 tance from the source. 



II. Using the same object, cast shadows upon the 

 screen by means of a candle and an incandescent electric 

 light. 



As before, adjust the candle and the electric light until 

 the two shadows are side by side and of the same bright- 

 ness. The light coming from the two sources must be then 

 equal in intensity. 

 Measure carefully 

 the distance of the 

 illuminations from 

 the corresponding 

 shadows and com- 

 pare these distances. FIG - 39- - Comparing lights. 



From the rule determined in I, calculate the number 

 of candles that would produce upon the screen an illumi- 

 nation equivalent to that of an electric light at the same 

 distance. This is called the candle power of the electric 

 light. 



EXPERIMENT 42. REFLECTION HOW LIGHT IS REFLECTED 



Fasten a sheet of paper to the table with thumb tacks, 

 and with a sharp pencil draw a line AB near the top of the 

 paper. Attach a mirror, or a piece of glass blackened on 

 one surface, to a block of wood and place this block on the 

 paper so that one edge of the mirror is coincident with the 

 line AB. 



