phere: the placing of artificial satellites in various orbits 

 around the Earth, carrying equipment to measure cosmic 

 rays from outer space, X-rays and ultra-violet light from the 

 Sun, the terrestrial magnetic field, the frequency of micro- 

 meteorites in space; and for use in studying continuously 

 the density of the atmosphere at great heights, and the shape 

 of the Earth: the intercomparison of very precise abso- 

 lute measurements of gravity made at numerous points on 

 all the continents: the practically continuous observation of 

 the Sun with equipment to detect and record solar flares 

 optically, and intensive observations of sunspots, promin- 

 ences and the solar corona using the latest optical and 

 radio techniques: the study of the geomagnetic field at the 

 Earth's surface, employing highly sensitive instruments like 

 the proton magnetometer: the investigation of radio-wave 

 propagation below and through the ionosphere, and its de- 

 pendence on solar activity: the obtaining of global data 

 on weather over both land and seas: the world-wide ob- 

 servation of earthquakes at many seismological stations: 

 and the obtaining of simultaneous observations in both 

 the Arctic and Antarctic to investigate correlations of polar 

 ionospheric fade-outs, aurorae, etc., in the two hemispheres. 

 Some of the outstanding results of these studies — data 

 collected during the IGY, when the Sun was at maximum 

 activity, was so extensive that it will take years to analyze 

 fully — ^were the discovery of the Van Allen radiation belt 

 surrounding the Earth (an enormous doughnut-shaped zone 

 of intense radiations lying some thousands of miles from 

 the Earth's surface, inside which particles from the Sun 

 become trapped due to the geomagnetic field); the discov- 

 ery of a close connection between aurorae in opposite polar 

 regions, and that the aurorae originate in the leakage of 

 charged particles from the Van Allen belt into the upper 



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