IGY IN RETROSPECT—ROBERTS 269 
munity to analyze so much material—masses of data not yet even 
collected in any one place. At this time we must be content, there- 
fore, with some broad views suggestive of the scope of the work, with 
an indication of some major findings and a few of the implications. 
It is also impractical in a short account to refer to the many indi- 
viduals and institutions deserving credit for what has been done. 
In practically all disciplines the IGY work served dramatically to 
raise new problems and to broaden our realization of the vastness of 
the unknowns into which we are, so to speak, poking exploratory 
fingers. The IGY produced many more questions than it answered. 
Lloyd Berkner has said that it is like coming from outer space and 
finding a new planet. 
The IGY investigations fit well into groupings based on major 
relationships between disciplines. One such scheme comprises: (a) 
The upper atmosphere, adjacent space, and solar influences; (0) the 
heat and water budget of the earth, comprising meteorology and re- 
lated aspects of oceanography and glaciology; and (c) the solid earth. 
PHYSICS OF THE UPPER ATMOSPHERE, SPACE, AND THE SUN 
Interplanetary space suddenly became important—and useful. The 
IGY showed us much about it. We learned that there is no definite 
end to the atmosphere. In its vague outer regions, at perhaps 3,000 
kilometers, it is almost indistinguishable from space itself. Solar and 
cosmic streams of elementary particles pass in undiminished intensity, 
forming with meteors the most important factors of the environment. 
The electrical and chemical activity of the upper atmosphere and of 
interplanetary space is due to X-rays and ultraviolet light, protons 
and electrons, meteors, and cosmic rays. There are present also elec- 
tric and magnetic fields due to the movements of charged particles, 
and everywhere there is gravity, the weakest of known forces but 
perhaps the most important in the universe. Atomic hydrogen is 
also everywhere, in densities of perhaps 6 to 600 atoms per cubic centi- 
meter. Previously unknown meteor streams were found, but the 
density of meteors and meteoritic dust, feared to imperil space 
vehicles, was found gratifyingly low. 
Within 10 earth diameters there exists an actual hydrogen atmos- 
phere, with a density at 500 kilometers as great as 100,000 atoms per 
cubic centimeter—this being ingeniously deduced from ultraviolet 
measurements made by nighttime and daylight rockets. Nearer the 
earth, atmospheric densities in the 200-500-kilometer band were found 
several times greater than previously supposed, as shown by observed 
retardation in the velocities of satellites. The density, moreover, 
exhibits strong variations supposedly due to the heating effect of 
particle collisions following solar bursts—this is suggested by satel- 
