288 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1959 
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Figure 2.—Transparency of the earth’s atmosphere to ultraviolet radiation. The 
curve gives the altitude in kilometers at which the intensity of extraterrestrial radi- 
ation is reduced by a factor of 2 at each wavelength. 
and with increasing altitude, the short X-rays would begin to come 
into view. However, the radiation in the 300 to 1,000 A. band would 
only be detectable at very great altitudes on the order of about 
200 kilometers. 
The expectations have largely been confirmed by developments of 
the past 10 or 12 years, thanks to the introduction of high-altitude 
rockets as a tool for astronomy. Shortly after the close of World 
War II, the United States initiated a program of scientific experi- 
mentation with a substantial number of V-2 rockets at the White 
Sands Proving Grounds. From the first, the observation of solar 
ultraviolet radiation received very high priority, together with cos- 
mic-ray experiments and those concerned with the measurement of 
pressures and temperatures in the high atmosphere. The first 
notable success was achieved by a group of scientists at the Naval 
Research Laboratory, headed by R. N. Tousey, who were successful 
in photographing the ultraviolet solar spectrum at a series of alti- 
tudes up to 55 kilometers. The flight was made on October 10, 1946, 
and the results obtained are shown in plate 1. This series of pho- 
tographs represents one of the great achievements in the history of 
observational astronomy, comparable in importance with the first 
map of the solar spectrum by Fraunhofer in 1814, with the invention 
of the spectroheliograph by Hale in 1891, and the coronagraph by 
