47 2 * 



the hemisphere of heaven. The light of the firmament 

 comes to us across the direction of the solar rays, and 

 even against the direction of the solar rays ; and this 

 lateral and opposing rush of wave-motion can only be 

 due to the rebound of the waves from the air itself, or 

 from something suspended in the air. It is also evident 

 that, unlike the action of clouds, the solar light is not 

 reflected by the sky in the proportions which produce 

 white. The sky is blue, which indicates a deficiency 

 on the part of the larger waves. In accounting for the 

 color of the sky, the first question suggested by analogy 

 would undoubtedly be, is not the air blue ? The blue- 

 ness of the air has, in fact, been given as a solution of 

 the blueness of the sky. But reason basing itself on 

 observation asks in reply, How, if the air be blue, can 

 the light of sunrise and sunset, which travels through 

 vast distances of air, be yellow, orange, or even red ? 

 The passage of the white solar light through a blue me- 

 dium could by no possibility redden the light. The 

 hypothesis of a blue air is therefore untenable. In fact, 

 the agent, whatever it is, which sends us the light of the 

 sky, exercises in so doing a dichroitic action. The light 

 reflected is blue, the light transmitted is orange or red. 

 A marked distinction is thus exhibited between the mat- 

 ter of the sky and that of an ordinary cloud, which lat- 

 ter exercises no such dichroitic action. 



By the force of imagination and reason combined we 

 may penetrate this mystery also. The cloud takes no 

 note of size on the part of the waves of ether, but reflects 

 them all alike. It exercises no selective action. Now 

 the cause of this may be that the cloud particles are so 

 large in comparison with the size of the waves of ether 

 as to reflect them all indifferently. A broad cliff re- 



