THE SKY 151 



shine like rubies. And all this splendor is evoked by the 

 simple mechanism of minute particles, themselves without 

 color, suspended in the air. Those who referred the ex- 

 traordinary succession of atmospheric glows, witnessed 

 some years ago, to a vast and violent discharge of vol- 

 canic ashes, were dealing with *'a true cause." The fine 

 floating residue of such ashes would, undoubtedly, be 

 able to produce the effects ascribed to it. Still, the mech- 

 anism necessary to produce the morning and the evening 

 red, though of variable efficiency, is always present in the 

 atmosphere. I have seen displays, equal in magnificence 

 to the finest of those above referred to, when there was 

 no special volcanic outburst to which they could be re- 

 ferred. It was the long-continued repetition of the glows 

 which rendered the volcanic theory highly probable. 



