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The Vela 3 satellites are in nearly circular orbits tilted at 60° to the ecliptic plane at geocentric distances of approximately 18.5 RE (earth radii). Thus the solar wind plasma can be sampled on both sides of the ‘bow shock,’ on both the dawn and dusk sides of the earth‐sun line, and at positions both in the ecliptic plane and far above and below it. An analysis of 13 crossings of the bow shock during July and August 1965, selected on both the dawn and dusk sides of the magnetosphere and with widely variable ecliptic latitudes show the solar wind bulk velocity to fall by ∼30% as the magnetosheath is entered. The density jumps by a factor of 2–5 typically, and the proton ‘temperature’ by a factor of ∼20. Multiple crossings of the shock front are common, and each crossing is easily recognized by the distinctly different characteristics of the solar wind plasma and magnetosheath plasma. For this time period typical average values of the bulk velocity and proton temperature near the shock front in the magnetosheath were 275 km/sec and 106°K. Thus the bulk velocity is larger than the mean thermal velocity, showing that most of the proton energy is associated with the ordered flow of the plasma around the magnetosphere.

Yield and angular distribution measurements on the T 3 (/>, 7)He 4 reaction have been made for protons up to 2.5 Mev. The yield indicates a resonance in the He 4 nucleus at a proton energy of about 2.5 Mev, giving an excited level at 21.6 Mev. The angular yield of the gamma-rays fits an A-\-B sin 2 # distribution very well, suggesting that the gamma-rays are due predominantly to a transition from the x Pi state to the 1 SQ state. An aluminum absorption curve for the secondaries produced in a lead radiator was taken, and a direct comparison made with the 17.5-Mev gamma-rays from the Li 7 (p, 7)Be 8 reaction, showing that the T 3 (/>, 7)He 4 gamma-rays are of higher energy.

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