24 



LIGHT 



book. Place upon 

 this a leaf, a piece of 

 lace, or any thin ar- 

 ticle, and cover with 

 the piece of glass. 

 Expose to the bright 

 sunlight until the 

 color of the paper is 

 a bronze. This color 

 must be learned by 

 experience. When 

 you think that the 

 color is right, re- 

 move the paper and 

 wash it for five min- 

 utes in running wa- 

 ter, or move it about 

 in a basin of water. The exposed part of the paper should 

 be a dark blue, while the rest should be a pure white. If 

 the blue color is not dark, it means that you did not leave 

 the paper in the sunlight long enough. If the light 

 part is not white, but is somewhat blue, it is because you 

 exposed the paper too long. You should repeat this ex- 

 periment at home until you can obtain clear white prints 

 upon a dark blue surface. 



Blue-print paper will also be used in Experiments 

 68 and 75. 



Review Questions, 6. 



1. If the sun should rise exactly in the south-east, 

 tell exactly where it would set. Why? 



