Spectrographic observations of the flash spectrum were made by the Kwasan Observatory at the total solar eclipse on 7 March, 1970. The integrated intensities of Fexiv ,~ 5303, Fex ~ 6374, and the continuum were measured on the spectrograms as a function of height above the Sun's limb. It was found that a large amount of emission in the coronal lines originates in the interspicular regions of the chromosphere. Analysis of the data yielded that the interspicular regions consist of coronal material of Te= 1.6 x 106-1.2 x 106 and log Ne=8.5-9.5, and that a decrease in T, and an increase in N~ occur with decreasing height.

The optical depth at the head of the Lyman continuum, rr~, is determined at a number of positions in three hedgerow prominences using spectroheliograms (5" x 5" resolution) of C m h 977, LC )t 896, and O Iv h 554 observed with the Harvard experiment on Skylab. At heights greater than 10" above the limb the maximum value of rH is 30 to 50, which occurs at the central part of the prominences. For one of the prominences the determination of Zla is found to be consistent with data from spectroheliograms of Mg x h 625. The degree of ionization of hydrogen is estimated from the intensity of LC h 896 at rH >> 1. In the central part of a model prominence Np/Nm-< 1.9 for a reasonable range of the electron densities, where Np and Nm are the proton density and the neutral hydrogen density, respectively.

Slitless flash spectrograms in heights below 8000 km above the solar limb were obtained by the

Based on the observations of the EUV spectroheliograms, the effective chromospherecorona transition region is assumed to be restricted in a small volume element in the boundaries of the supergranular network. The center-to-limb variation of the quiet Sun at cm and dm wavelengths is analyzed to determine where the transition region is located in the network boundaries.Expressions are derived for the theoretical center-to-limb variation of the hypothetical brightness temperature only from the transition region, taking into account the orientation of the spicules. Comparison with the observations shows that the spicule-sheath model (Brueckner and Nicolas, 1973) and the hot plagette model (Foukal, 1974) are not compatible with the observations, because the limb brightening predicted by these models is too great.A new picture is therefore proposed that thin platelet transition regions are placed on top of the chromosphere and scattered between the network boundaries (the platelet transition-region model). This model is in accord with the observed center-to-limb variation of the radio emission.

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