Roebling Fund 
PERIODS RELATED TO 273 MONTHS OR 
22% YEARS 
By C. G. ABBOT 
Research Associate, Smithsonian Institution 
This period was discovered in the variation of the measures of the 
solar constant of radiation, made daily by the Smithsonian Astro- 
physical Observatory from 1920 to 1952. It was first glimpsed in 
1935,' and noted in various terrestrial phenomena, such as tempera- 
tures, precipitation, width of tree rings, and levels of lakes. The level 
of Lake Huron, since 1837, has followed related periods of about 23, 
46, and g1 years. I ventured, in 1938, to predict droughts during the 
1950’s, the 1970's, and the 2020’s, based on recurring periodic de- 
pressions of the level of Lake Huron. The first of these predictions 
is now verified. 
1, PERIODS FOUND IN SOLAR-CONSTANT MEASUREMENTS 
The “solar constant of radiation” is the term in use to describe 
quantitatively the intensity of the sun’s radiation, as it would reach 
points in space outside the earth’s atmosphere, at the earth’s mean 
distance from the sun. 
Smithsonian measurements over many years, made at stations rang- 
ing from sea level to 14,400 feet altitude, and supplemented by auto- 
matic records at 15 miles of elevation from sounding balloons, yield 
as the value of the solar constant 1.946 calories per square centimeter 
per minute. A recent revision by F. S. Johnson,? in which he used 
the latest data from high rocket flights to improve the Smithsonian 
estimates in the extreme ultraviolet spectrum, yielded the value 2.00 
cal.+0.04 cal. His value differs from the Smithsonian value by little 
beyond the probable error of either one. For purposes of estimating 
solar periodic variations, this small difference as to the basic value is 
inconsequential. 
1C. G. Abbot, Solar radiation and weather studies, Smithsonian Misc. Coll., 
vol. 94, No. 10, 1935. 
2 Journ. Meteorol., vol. 11, No. 6, December 1954. 
SMITHSONIAN MISCELLANEOUS COLLECTIONS, VOL. 134, NO. 1 
