282 BREWER 



that there is enough suspended matter, even there, to make 

 a luminous sky on which shadows can be cast. The night 

 we steamed across from the Asiatic to the American coast, 

 just below Bering Strait, the southern sky was cloudless, 

 there was no moon, and the earth shadow was very dis- 

 tinct. It was a grand arch of deep blue which slowly 

 rose and crept along the southern sky, attaining at mid- 

 night the height of thirty or forty degrees. It was very 

 much higher than I have ever seen the shadow in lower 

 latitudes. It was very distinct as to shade, although not 

 so sharp in outline as we see at home. There was no 

 tinge of rose or purple, although we had some red and 

 crimson clouds in the north. The arch moved westerly 

 across the southern sky and vanished before it sank to the 

 horizon. 



It was discovered, some twenty years ago, that when 

 the vapor of water condenses and forms fog or cloud, it 

 must have dust particles to condense upon. Without dust 

 there is no fog nor cloud ; the more abundant the parti- 

 cles, the denser the fog or cloud may become. This dis- 

 covery has attracted much attention among meteorolo- 

 gists, and ingenious methods have been devised to count 

 the number of dust-particles contained in a measured 

 quantity of air. Thousands of such countings have been 

 made. The air has been examined in many countries and 

 many places over sea and land, on mountains and in 

 valleys, in cities and in the country. Numerous tables 

 giving the numbers found in various localities, have been 

 published in scientific works. It is enough here to say, 

 that the number varies greatly, ranging from a very few 

 in the purer air on high mountains to many thousands 

 of particles in a single cubic inch of city air, but I am not 

 aware that any such observations have ever been made in 

 any high latitude. The vast arctic region is mostly cov- 

 ered by water, ice or snow, and with its scanty population 



