IGY IN RETROSPECT—ROBERTS Zt 
disturbance. The play of magnetic fields in the upper atmosphere 
induced potentials in transatlantic cables as great as 2,650 volts. 
From the moment of discovery of the original flare until the return 
of normal conditions several days later, all IGY scientists interested 
in space and the upper atmosphere had unexcelled opportunity to 
make coordinated observations, demonstrating the high value of the 
synoptic approach. 
Artificial radiation effects —An event of great interest, but not part 
of the IGY, showed, on August 1, 1958, that atomic bursts in the 
ionospheric regions are capable of producing artificial radiation 
and other widespread effects matching those of Nature itself. <A 
nuclear explosion was produced by the United States in the ionosphere 
over the Pacific near Johnston Island, and within 1 minute a visible 
aurora was observed at Samoa—the first time in history! Simultane- 
ously, Hawaii was aroused by a brilliant flash of hght. Strong mag- 
netic disturbances were recorded on the magnetographs at Honolulu, 
Samoa, Palmyra, Fanning, and Jarvis Islands. Radio blackouts of 
circuits over a large Pacific Ocean area persisted for one or more 
days. The radiation was detected and reported during many hours 
by the earth satellite Explorer IV during its passages over the area. 
Another such explosion at lower height 11 days later produced some- 
what similar results. 
A significant circumstance is that the location of the blasts and the 
vicinity of the Samoan aurorae are conjugate points respecting the 
geomagnetic lines of force. Charged particles introduced into the 
field at one of the points would predictably reenter the atmosphere at 
the other, as occurred at Samoa. Such controlled tests tell much about 
hitherto inaccessible phenomena. 
A similar but even more dramatic demonstration was made, by 
definite design, in late August and early September 1958, when three 
small nuclear devices were exploded by the United States above the 
South Atlantic in the near vacuum of a region of relative minimum of 
natural radiation between the Van Allen layers. Immediately there 
were seen streaks of auroral luminescence along the magnetic lines of 
force, and a brilliant aurora was observed at the conjugate point near 
the Azores, where the particles, after spiraling along the lines out to 
distances as far as 6,500 kilometers into space, reentered the atmos- 
phere. Theoretical predictions of the external figure of the geo- 
magnetic field were verified. Following the now famous predictions 
of N. C. Christofilos, energetic particles immediately dispersed in a 
shell determined by the geomagnetic field, where they persisted during 
the battery lifetime of the satellite Explorer IV until late September. 
For the first time in history worldwide measurements were made on a 
completely controlled geophysical phenomenon, wherein a known 
