CHAPTEE XVII. 



THE SKY AND ITS COLOB. 



In the chapters on light in Vol. II. it will 

 be stated that we see all objects by a reflected 

 light, except those that are self-luminous, 

 such as the sun or any other source of light. 

 We see the moon and many of the planets 

 entirely by reflection. There are myriads 

 of smaller objects, too small to be seen 

 as such, even under a microscope, that still 

 have a power to reflect light that is sensible to 

 our vision. The air surrounding the globe is 

 literally filled with these microscopic light re- 

 flectors. They serve to give us a diffused 

 light which enables us to see clearly all visible 

 objects. We have all noticed the effect of a 

 single electric arc light, situated at a distance 

 from any other source of light, and how it 

 casts extremely dark shadows and very high 

 lights ; so much so that it is difficult to see an 

 object perfectly in this light, because the part 

 of an object that is under the direct rays of 

 the lamp is so highly illuminated that the 

 shadow, by comparison, has the effect of 



134 



