140 FRAGMENTS OF SCIENCE. 



white. The sky is blue, which indicates a deficiency on part 

 of the larger waves. In accounting for the color of the sky, 

 the first question suggested by the analogy would undoubt- 

 edly be, Is not the air blue ? The blueness 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 white solar light through a blue 

 medium could by no possibility redden the light. The hy- 

 pothesis 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 matter of the sky 

 and that of an ordinary cloud, which exercises no such di- 

 chroitic 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 com- 

 parison with the size of the waves of ether as to reflect them 

 all indifferently. A broad cliff reflects an Atlantic roller as 

 easily as a ripple produced by a sea-bird's wing ; and in the 

 presence of large reflecting surfaces, the existing differences 

 of magnitude among the waves of ether may disappear. 

 But supposing the reflecting particles, instead of being very 

 large, to be very small, in comparison with the size of the 

 waves. In this case, instead of the whole wave being 

 fronted and in great part thrown back, a small portion only 

 is shivered off. The great mass of the wave passes over 

 such a particle without reflection. Scatter, then, a handful 

 of such minute foreign particles in our atmosphere, and set 

 imagination to watch their action upon the solar waves. 



