ATMOSPHERE 283 



and its abundant storms to wash the atmosphere, the 

 amount of dust in its air must be very much less than in 

 the air over more densely inhabited countries and in 

 warmer climates. A few years ago I made a series of 

 observations on atmospheric appearances along the coasts 

 of Labrador and Greenland and in Baffin Bay up to the 

 Arctic Circle. All the phenomena there are in accord- 

 ance with what we might expect from an atmosphere 

 containing only fine dust and vastly less in quantity than 

 is found in all warmer latitudes. I made similar observa- 

 tions on the aspects of the sky and air every day of the 

 Harriman Alaska Expedition. 



Westerly winds prevail along the western coast of 

 North America from Mexico northward. Coming over 

 the broad Pacific, they lose on the way much of the dust 

 that had been gathered from other regions. This explains 

 the cause of the very clear air of California and the other 

 Pacific States. Near the coast the air when dry and with- 

 out fog is marvelously clear. From California northward 

 to Alaska, forest fires later in the season often make a 

 very smoky atmosphere. As we steamed up the inland pas- 

 sage northward, the blue haze, due mostly to smoke, rap- 

 idly diminished, its softening effects upon the landscapes 

 grew less and less, and from Glacier Bay on our way out 

 until we reached Yakutat on our return, we saw practi- 

 cally none of the effects of a smoky or a dusty atmosphere. 

 We sometimes had a haze when the air was nearly satu- 

 rated with moisture, but it was never a blue haze always 

 white like a faint transparent fog. When the air was dry, 

 the atmosphere was then always very transparent and dis- 

 tant objects were marvelously distinct. When the moon 

 rose, it was bright and white and without color. I watched 

 its rising several times when it was as white and clear at 

 the horizon as it was when it reached mid-sky, without a 

 tinge of color and with no perceptible diminution of its 



