SOLAR VARIATION AND WEATHER—ABBOT 121 
constant of radiation. The presence of areas of faculae, hotter and 
more radiative than the adjoining solar surfaces, will also, as they 
march around with the sun’s rotation, produce variations of the solar 
constant. 
THE EARTH’S TEMPERATURE 
The earth as a planet is kept in its present approximately constant 
state at the mean temperature of 14° Centigrade by the balance of its 
receipt of heat from sun rays against the outgo of heat caused by the 
earth’s emission to space. This earth emission arises in the invisible 
long-wave rays which lie between the gamut of visible light and the 
gamut of rays of very great wave length, which are used in radio 
transmission. To fix ideas in terms of the centimeter, the unit of 
length in the metric system, visible light rays have wave lengths 
between 4 and 7 hundred-thousandths (0.00004 and 0.00007), earth rays 
between 4 and 40 ten-thousandths (0.0004 and 0.0040), and radio rays 
between 10 and 1 million (10 and 1,000,000) centimeters. But all of 
them are of the same fundamental nature of transverse vibrations. 
Since the earth’s mean temperature keeps within fairly definite 
bounds because the total receipt of heat from the sun is in approxi- 
mate equilibrium with the total escape of heat from the earth, it is 
plain that if the sun’s contribution should change permanently, the 
earth’s mean temperature would change to a new state of equilibrium. 
However, the sun is so immense that no considerable general change 
of this kind is to be apprehended in thousands, or even millions, of 
years. Nevertheless, in what follows it will be shown that temporary 
changes of the order of 1 percent do frequently occur in the sun’s 
output, and that these affect weather locally so much that solar changes 
must be rated as major meteorological factors. 
SMITHSONIAN SOLAR-CONSTANT WORK 
_ For many years the Smithsonian Institution has maintained ob- 
servatories for measuring the intensity of solar rays. Our best sta- 
tion is Montezuma, in the Atacama Desert of northern Chile. It 
is located on a mountain 9,000 feet high, where years frequently go 
by without a drop of rain. The observers must be supplied from the 
city of Calama, 12 miles away, with water, as well as all other ne- 
cessities. The sun shines from an unclouded sky on nearly 80 percent 
of all days. As it is very trying to the nervous system to live in such 
isolation under constantly cloudless skies, it is necessary to relieve the 
observers at intervals of 2 or 3 years. Indeed, great loyalty to the 
objects of the work, excellent ability as observers, much tact in dealing 
with the people of the vicinity, and conscientious honesty and industry 
are absolute requirements of the observers for the successful operation 
