ATMOSPHERE 281 



tographs have been taken of the shadows of Pikes Peak 

 and of Mount Hood and perhaps of other mountains. 

 When seen under the best conditions, this shadow consti- 

 tutes a phenomenon of indescribable impressiveness. I 

 have a most vivid recollection of such a scene from one 

 of the high volcanic cones of northern California, which 

 may be cited as an illustration. We had climbed the peak 

 in the night and were on the summit until midday. The 

 sky was absolutely cloudless and the air still and excep- 

 tionally clear, having been purified by a recent storm. 

 Never before nor since have I had a wider view. Points 

 two hundred miles distant were sharply defined on the 

 horizon, yet, even in that clear air, there was dust enough 

 to serve as a screen on which the grand picture was 

 thrown. As the sun rose, a giant spectral mountain ap- 

 peared against the opposite sky. It was of deep cobalt 

 blue sharply defined against the lighter ' azure-blue ' of 

 the sunlit air about it. An optical illusion greatly mag- 

 nified its size. Owing to the curvature of the earth's sur- 

 face, it reached high in the sky and far above the Coast 

 Ranges on the western horizon. It was much higher than 

 any real mountain on earth, but as the sun mounted higher 

 the spectre sunk lower until it disappeared. 



The shadow of the earth itself may often be seen in 

 the eastern sky on a clear evening. Just after the sun dis- 

 appears, a dark band appears along the opposite horizon 

 and slowly creeps upward. It is darker blue in color than 

 the sky above it and is often bordered on its upper edge 

 by a fringe of faint rose-color which sometimes takes on 

 a distinctly purple hue. 



When farthest north on our Alaska cruise, the earth 

 shadow was especially interesting, and its appearance in- 

 dicated the great purity of the air there as related to dust 

 or smoke. The long Arctic twilight is sufficient evidence 



