198 
INTENSITY 
RELATIVE 
ANNUAL REPORT SMITHSONIAN INSTITUTION, 1948 
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WAVELENGTH A. 
PRELIMINARY SOLAR 
INTENSITY DISTRIBUTION 
10 OCTOBER, 1946 
Ficure 5.—Solar intensity distribution obtained from spectra of October 10, 1946. 
(These data are preliminary since the analysis of all spectra is not yet complete.) 
Two successful experiments have 
been conducted to date in solar spec- 
troscopy with the result that nearly 100 
spectra have been obtained at vari- 
ous altitudes up to 160 km. (24, 25). 
The spectrograph (similar ones were 
used in the two flights) was arranged 
to record only the wave lengths below 
3400 A.; in some of the spectra ob- 
tained at higher altitudes radiation 
was recorded down to 2100 A. Anal- 
ysis of these spectra has produced the 
following results. 
1. Solar spectral-energy distribution — 
The curve of average radiant energy 
as a function of wave length—the so- 
called black-body curve of the sun— 
was extended from the previous limit 
of 2900 A. to 2200 A. shown in figure 5. 
The ultraviolet intensities are much 
less than had been predicted (26). 
2. Fraunhofer line analysis—A large 
number of fully and partly resolved 
absorption minima were observed in 
the region between 2950 and 2300 A., 
as shown in plate 5, figure 1. Nearly 
