The European Space Research Organisation put its first satellite into orbit in March 1968 and was successful with two more before the end of that year. It was not entirely surprising therefore that the third annual ESLAB/ESRIN Symposium should in some way deal with the results obtained. This book is the Proceedings of that Sym­ posium which, for reasons which Dr. Trendelenburg explains in the introductory talk, concentrated on intercorrelating phenomena occurring during solar events and in particular during the event of 25 February 1969. It is generally acknowledged that space data could yield a much more fruitful harvest if measurements taken simulta­ neously in different regions of space could be compared and the detectors inter­ calibrated. ESRO therefore sought right from the start to encourage this comparison of data. The first two days of the Symposium (16 and 17 September 1969) were devoted to review lectures on inter-related phenomena occurring on the sun, through inter­ planetary space and the magnetosphere right down to the earth's ionosphere. The last two days were used to hear papers presenting results obtained from the ESRO and certain U. S. S. R. and U. S. A. satellites during the solar events around 25 February 1969. The Proceedings published here follow the same sequence as the Symposium presentations. Because of the short time interval between the solar event and the Symposium, some of the data presented in the second part must be regarded as preliminary.

Table of Contents:
1. Summary Lecture.- A Survey of Interplanetary and Terrestrial Phenomena Associated with Solar Flares.- 2. Solar Particles and Electromagnetic Radiation.- High Energy Flare Radiation.- Satellite Observations of Solar Cosmic Rays.- Propagation of Solar and Galactic Cosmic Rays of Low Energies in Interplanetary Medium.- Particle Event Forecasting.- Proposed Solar Proton Event Classification System.- 3. Solar Wind Variations During and After Solar Events.- Solar Wind Disturbances Associated with Solar Activity.- Variations of Solar Wind Fluxes Observed on Board Venera-5 and Venera-6 from January 21 to March 21 1969, and Pulsations of the Earth’s Electromagnetic Field Caused by these Variations.- Magnetic Field Variations in Interplanetary Space.- 4. Bow Shock Variations Following Solar Events.- Plasma Measurements Across the Bow Shock and in the Magnetosheath.- Interaction of Solar Energetic Particles with the Earth’s Bow Shock and Magnetopause.- Magnetic and Electric Field Changes Across the Shock and in the Magnetosheath.- 5. The Magnetosphere During and After Solar Events.- Solar Particle Observations over the Polar Caps.- Access of Solar Particles to Synchronous Altitude.- Entry of Low Energy Solar Protons into the Magnetosphere.- Trapped Particle Population Changes Associated with Solar Events.- Geomagnetic Storms at ATS 1.- Magnetospheric Electric Fields.- 5A. The Magnetotail.- Experimental Observations in the Magnetotail during an Interplanetary Disturbance.- Tearing Instabilities in the Magnetosphere.- 6. Some Ionospheric Effects Following Solar Events.- Current Problems in Polar-Cap Absorption.- Interdisciplinary Investigations of the Auroral Phenomena.- Aspects of Auroral Morphology.- Acceleration and Precipitation of Van Allen Electrons DuringMagnetospheric Substorms.- 7. Satellite and Rocket Results for the February 25, 1969 Event.- to the ESRO Spacecraft ESRO-II/IRIS, ESRO-I/AURORAE and HEOS-1.- Ground Observations of the Solar Event of February 25, 1969.- Substorm Influences on VHF Continuous Wave Auroral Backscatter.- X-Ray Observations between 1 and 55 Å of the February 25th Flare.- The Solar Particle Event of February 25, 1969.- Interplanetary Magnetic Field Measured by Pioneer 8 during the 25 February 1969 Event.- Observation of Solar Wind Discontinuities from February 24 to February 28, 1969.- Observations of the Spectra and Time History of Protons in Interplanetary Space, February 25–28, 1969.- Solar Cosmic Ray Increase on 25 February-5 March, 1969 According to Measurements from Venus-5 and Venus-6 Space Probes.- Low Energy Proton Measurements in Interplanetary Space on Board the HEOS-1 Satellite.- The Solar Particle Events of 25 February, 1969. Directional Measurements of Solar Protons with Energies Greater than 360 MeV on HEOS-1.- Observations Recorded by the Leeds University Cosmic Ray Detector on Board the ESRO-II Spacecraft during the Solar Flare of February 25th 1969.- ESRO-I Satellite Observations of 1-30 MeV Protons During the 25th February 1969 Solar Event.- Rocket Measurements of Protons and ?-Particles During the February 25, 1969 Solar Event.- Rocket Observations of Protons and ?-Particles at Andøya after the Solar Flares of 24th–25th February, 1969.- Electron Density Observations During the PCA Event of 25 February, 1969.- Rocket-Borne D-Region Probe Measurements.- Electron Density Measurements in the Thermal Plasma of the Magnetosphere Using a Langmuir Probe.- Ionospheric Measurements by the ESRO-I Satellite During the February 25th 1969 Solar Proton Event.- ESRO-I SatelliteObservations of 45–450 keV Electrons During the Period 24th February–3rd March, 1969.- ESRO-I Measurements of Low-Energy Auroral Particles from February 23 to March 2, 1969.- An Observation of the February 26, 1969 Interplanetary Shock Wave.- The Association of Energetic Storm Particles with Interplanetary Shock Waves.- GM Observations of Auroral Particles and Ground Observations During the February 25th Solar Event.- Observation of Low-Energy Solar Protons During the February 25, 1969 Event.- High Energy Solar Electrons.- OGO-5 Measurements of Electrons Above 500 MeV.- 8. Lecture in Conclusion.- Suggestions for Future Observations.- Index of Names.