Published online by Cambridge University Press: 25 April 2016
In July 1967 and June 1968 observations of the central intensity variation in several chromospheric lines were obtained by P. R. Wilson and myself at Sacramento Peak Observatory, New Mexico using the 16-inch coronagraph coupled with the high-dispersion Littrow Spectrograph. Observations in the MgB lines (λ5184, 5173, 5167 Å) were obtained the first summer whilst the NaD lines (λ5889, 5896 Å) were studied in the second. Table I shows the mean heights in the solar atmosphere at which it is thought these lines are formed.