1884. 61 Trans. N. Y. Ac. Sci. 



body of the stream tend to keep the particles of silt long in suspen- 

 sion. 



Mr. B. B. Chamberlin referred to the lemon-yellow color which 

 frequently succeeded to the red glow, and produced very interesting 

 results, generally rendering the lighter clouds pea-green, and the 

 heavier ones olive. A little later he had noticed that the steam from 

 the steamers in the harbor assumed a beautiful lavender color, while 

 the smoke from the chimneys was colored like the clouds. 



The President supported the view that the red glow was due to the 

 diffusion of volcanic dust rather than cosmic matter, and gave several 

 illustrations of the abundance of particles of solid substance in the 

 atmosphere. Smoke, which consists of minute particles of carbon, 

 sometimes covers whole States, and obscures the sun's light. During 

 the last summer he had traversed a great area on the Pacific coast, 

 where, for several months, smoke from forest fires in a specially dry 

 season had concealed all distant objects. The blue color of the sky 

 is supposed to be due to floating particles, and the haze which pre- 

 vails for days and weeks with a cloudless sky, in autumn, is nothing but 

 dust and smoke. The accumulation of volcanic dust on ships at sea, 

 hundreds of miles from the craters from which it had issued, is an 

 exhibition of the possible wide diffusion of such material. 



The system of circulation of the atmosphere favors the spread over 

 the whole world of dust thrown into the air in the tropics. The move- 

 ment of the surface from west to east in the rotation of the globe is 

 about one thousand miles an hour. The atmosphere, resting on the 

 earth, moves with it, but not quite so fast. It lags behind at the sur- 

 face five or six miles an hour ; at a greater elevation, perhaps much 

 more. This causes the great equatorial wind current, which flows 

 from east to west in a belt, some thirty degrees in width, along the 

 equator. At the same time the air in the equatorial belt is heated, 

 rarified, and rises, to be replaced by the cooler northeast and south- 

 east trade-winds which blow in along the surface of the sea. This 

 causes a great movement of the atmosphere from the equator in a 

 series of vertical circles toward the poles. As a consequence of this 

 system of atmospheric circulation, whenever a discharge of dust takes 

 place from a volcano like Krakatoa, in the equatorial belt, the dust 

 is, in the first place, carried upward in the ascending currents of the 

 heated zone, is carried westward by the equatorial current, and dis- 

 tributed toward the poles by the outflow from that zone. Hence, it is 

 easy to see that the dust of Krakatoa might in time pervade the atmos- 

 phere over all the earth's surface. 



