From an investigation of spectra in a magnetically sensitive (26173, g --2.5) and insensitive line (25576, g = 0), we derived the following properties for a symmetrical sunspot: (a) The magnetic field strength varies with the distance Q(O ~< 1) from the sunspot center like H(O) = H(0) (1 § 02) -I. (b) The zenith angle of the magnetic field varies like 90~ From this and from H(0)we find a height gradient of 0.5 gs/km at 0 --0. (c) The equivalent width and the half width of 25576 show an increase in penumbral regions of maximum Evershed flow. Most likely this is due to a combination of inhomogeneities in the Evershed flow and 'microturbulence'.(d) We find the magnetic field strength to be larger in the dark interfilamentary regions of the penumbra. These regions move downwards with respect to the bright filaments and probably have a more horizontal magnetic field.(e) In a weak ligtlt bridge and in extensions of bright penumbral filaments into the umbra, we find a decrease of the magnetic field strength, and a more horizontal field direction with respect to the umbral surrounding.(f) In umbral dots and in the light bridge we find a relative upward motion.

The present status of observations regarding the solar differential rotation is reviewed from contributions published in the last two decades. The paper does not deal with the theory; it mentions theoretical aspects only where they are needed to guide and to understand observational efforts and results.

We address the magnetic field structure of solar pores. The data were obtained at the Gregory Coud~ telescope at Izafia using the AT1 CCD camera system to observe pores with three spectral lines: one magnetically sensitive line, recording all 4 Stokes profiles, and two g = 0 lines where only the intensity profiles were measured. The data reduction included the standard procedure (removing dark current and flatfielding) as well as destretching of the polarimetric spectra and removing the non-magnetic straylight by means of a 2-d deconvolution of the observed intensity variation using a Lucy-Richardson restoration algorithm. In the following analysis we first determined the temperature-and pressure stratification of the pore using the g = 0 lines and then applied an inversion of the Stokes profiles to get the parameters of the magnetic field. Across the pore we find a strong variation of the resulting field strength as well as of the inclination and the azimuth, consistent with the assumption of a canopy forming in the higher atmosphere.

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The appearance of arc component of a normal Zeeman triplet in sunspot umbrae, while close to the center of the solar disk, can partly be explained by light scattered from the photosphere into the umbrae. After correction for this, there still remains a residual ~ component which has often been taken as evidence for the presence of transverse field components in the center of regular, unipolar sunspots.Observations in opposite circular polarizations show, however, that this apparent rc component has a Zeeman splitting of its own opposite to that of the main Zeeman splitting (S~vERNY, 1959; DEVBNER, 1967 DEVBNER, , 1969SHEELEY, 1968). BECKERS and SCHR6TER (1968b) suggested that this behaviour be interpreted in terms of inhomogeneities in the magnetic field of sunspot umbrae and that these inhomogeneities consist of a strong field component (~ 3000 gs) and a weaker opposite field component (~200 gs). Recently HENOUX (1968) gave a different explanation for the appearance of the 'artificial rc component'. He showed that for lines which are saturated, the line profiles for circular polarized light when computed with Unno's theory can look like those shown in Figure la.In order to study the effect of saturation on the shape of the line profile of a normal Zeeman triplet, we computed with Unno's theory the line profile for circular polarized light for various absorption coefficients in the line center (r/o) and various inclinations of the field vector to the line of sight (7). The results of the computations are shown in Figure 2, whereas Figure 3 shows the corresponding difference curves between left-and right-hand circular polarized spectra, e.g., the variation of the V-Stokes parameter within the line. These curves behave as one would expect, having a constant sign on the blue side of A2---0 and an opposite sign on the red side. The difference curves show an increase of separation of the two peaks for large values (leading to an apparently larger magnetic field). This is due to the overlapping of the absorption in the violet part of the o-r-component with that in the red part Solar Physics 7 (1969) 22-25; 9 D. Reidel Publishing Company, Dordrecht-Holland