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{d) From a rather small number of observations by Guthnick on the 
brightness of the planet Saturn, it appears that equal fluctuations of the 
brightness of the planet attend observed fluctuations of the radiation of 
the sun. This result, however, requires that allowance shall be made for 
the rotation of the sun to take into account the difference in heliographic 
longitude between the earth and Saturn. 
{e) Various observers, notably Clayton, Arctowsky, Helland-Hansen, 
and Nansen, have published results showing the correlation between 
terrestrial temperatures, and other meteorological phenomena, and our 
observed variations of the sun. 
(/) Bauer found a correlation between solar variation and the varia- 
tions of terrestrial magnetism. 
5. Atmospheric Transparency. — We have determined the transparency 
of the earth's atmosphere to solar radiation at stations ranging from sea- 
level to 4,420 meters for nearly 40 wave-lengths. We have observed the 
dependence of the atmospheric transparency on humidity and volcanic 
dust, and its variation from month to month, and from year to year. 
Since atmospheric transparency is associated, by Rayleigh's theory of 
the blue of the sky, with the number of molecules per cubic centimeter of 
air, our results have led to an independent value of this constant for which 
Mr. Fowle finds 2.70 X 10^^ molecules per centimeter cube in air at 
standard temperature and pressure. 
6. Brightness of the Sky. — Measurements have been made of the bright- 
ness of the sky by day, as a whole and in parts, and the variation of it from 
sea-level to 4,420 meters, as well as the effects upon it of the presence of 
clouds. 
Mr. Aldrich took advantage of the presence of the Balloon School at 
Arcadia, near Mt. Wilson, to observe the reflecting power of clouds as 
formed there in a great level sheet some 500 meters high. From his 
results, it appears that if the earth were completely enshrouded in a smooth 
layer of cloud its reflection would be approximately 77 per cent. 
7. Long-wave Ray Investigations. — Mr. Fowle carried on spectrobolo- 
metric investigations of the rays of the Nernst glower as affected by the 
humidity and carbon dioxide prevailing, in very long absorbing tubes at 
atmospheric pressure and temperature. These measurements covered 
the spectrum in the region of the earth's emission up to a wave-length of 
nearly 20 microns. The investigation included the distribution of the 
rays in the solar spectrum in this region. Many measurements have been 
made also on the absorption and reflection of liquid water, and many other 
terrestrial substances and of their degree of transparency to long-wave 
rays. 
9. Distribution of Radiation over the Sun's Disk. — It was previously 
known that the brightness of the sun's disk falls off towards the edges, but 
