296 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1959 
rocket photograph of the ultraviolet solar spectrum, Dr. Lyman 
Spitzer pointed out that, as seen from a satellite, the sun rises and 
sets at frequent intervals. At these times, the sun’s rays would have 
to traverse the upper atmosphere at different heights before reaching 
the satellite and would be partially absorbed. Measurement of the 
changes in the intensity of the spectrum with time would provide 
a very sensitive determination of the densities of the different types 
of atoms in the earth’s upper atmosphere. It is now known that the 
ultraviolet spectrum of the sun contains emission lines of oxygen, 
nitrogen, and hydrogen, and that these lines are absorbed by the 
same kinds of atoms in the earth’s atmosphere. Now the total den- 
sity of the upper atmosphere can be derived from the changes in the 
orbit of a satellite caused by frictional drag. If the individual par- 
ticle densities are also known from spectroscopic measurements, it 
would be possible to calculate the change of temperature with height 
at great altitudes and so to answer the question as to the extent of the 
thermosphere. This is the region above the mesopause in which the 
temperature increases with height from about 200° Kelvin at 100 
kilometers to about 1,100° Kelvin at 300 kilometers. It is not known 
whether, above 300 kilometers, the atmosphere becomes isothermal, 
or whether, as Chapman suggests, the temperature continues to rise 
until the earth’s atmosphere merges with the very hot gas of the 
solar corona at a distance of several earth radii. The possible de- 
tection of hydrogen and the measurement of its density at great alti- 
tudes would be of particular interest. This could be accomplished 
by monitoring the intensity of the solar Lyman-« line. 
The arrival of solar-ejected particles, chiefly protons and electrons, 
at the earth is evidenced by their trapping in the Van Allen radia- 
tion belts, by the occurrence of magnetic storms and auroral displays, 
and by the observation of enhanced cosmic-ray intensity following 
solar flares. During 1959, physicists at the University of Minnesota, 
led by Ney and Winckler, found, by measurements from balloons, 
that the earth is being bombarded by bursts of low-energy 
cosmic rays with a frequency and intensity far greater than had been 
known or expected. The solar origin of these bursts seems un- 
disputed. At the same time, evidence for the ejection of particles 
from the sun is best adduced from the observation of bursts of radio 
noise at very low frequencies. J. P. Wild in Australia has shown 
that many great solar flares are accompanied by bursts of radio emis- 
sion which appear first at the higher frequencies, greater than about 
200 megacycles, and then drift progressively toward the lower fre- 
quencies. Wild has interpreted these bursts as arising from corpuscu- 
lar streams ejected from the region of solar flares at very high speeds 
up to 100,000 kilometers per second. The high frequencies come from 
