We used very-long-baseline interferometry (VLBI) to measure the deflection by the Sun of radio waves emanating from distant compact radio sources. This bending is characterized in the parametrized post-Newtonian formalism by gamma, which is unity in general relativity. Using a large geodetic VLBI data set, we obtained gamma=0.9998(3)+/-0.0004(5) (estimated standard error). We found no systematic biases from our analysis of subgroups of data.

SummaryThe pulse method of radio sounding has been used at 1· 75 Mc/s to detect low ionospheric regions whose voltage reflection coefficient exceeds 4 X 10-6 • Observations from February to July 1955 have revealed reflections, from 95 km vertical height and of day-time occurrence only, which are believed to originate in the lower E region. A region with a lower boundary predominantly at 85 km has been found to exist continuously, and previous suggestions as to its meteor origin are queried. A series of complex partial reflections have been detected during day-time only down to 53 km, with significant heights near 75, 67, and 55 km. The occurrence and strength of these lower reflections increases markedly during winter.From records of high absorption conditions during winter days, a connexion between the decrease in strength of E region reflections and the increase in strength of partial reflections between· 66 and 88 km approximately is demonstrated.