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The properties of rapidly changing inhomogcneities visible in the t[ and K lines above sunspot umbrae are described. We find as properties for these 'Umbral Flashes':(a) A lifetime of 50 see. The light curve is asymmetrical, the increase is faster lhan the decrease in brightness.(b) A diameter ranging from the resolution limit up to 2000 kin. (c) A tendency to repeat every 145 sec. (d) A 'proper motion" of 40 kin/see generally directed towards the penumbra. (e) A Doppler shift of 6 km/'sec. (f) A magnetic field of 2100 G. (g) A decrease in this field of 12 G/sec. This decrease is probably related to the flash motion.(h) At any instant an average of 3-5 flashes in a medium-sized umbra. A weak feature often persists in the umbra after the flash. This post-flash structure initially shows a blue shift, but 100-120 sec after the flash, it shows a rapid red shift just before the flash repeats.

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.

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