Observations of the Zodiacal Light from a Very High Altitude Station: II. Electron Densities in Interplanetarry Space

Abstract

The evidence for and against the existence of an interplanetary gas is reviewed. Spectra of the zodiacal light obtained in 1958 at the high altitude station of Chacaltaya (height 17 100 ft) in Bolivia with a dispersion of 38 A/mm are described and used to investigate the concentration of free electrons in the plane of the ecliptic at 1 A.U. from the Sun. No electrons could be detected along a line of sight at elongation 32° and it is deduced that the electron density at 1 A.U. is not greater than 120 cm ⁻³ .