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 witha 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. Asa 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. 
