Abstract : Twenty-one-cm absorption spectra have been obtained for 12 radio sources using conventional techniques. Six of these sources were also studied with a hydrogen-line interferometer. Differences in the profiles obtained by the 2 methods give information on the structure and temperature of the HI clouds seen in absorption. Estimates of the angular sizes of 4 clouds based on these differences lead to an average diameter of 13 parsecs. In some cases it has been possible to find an upper limit to the temperature of the clouds somewhat lower than the generally assumed 125 K. A temperature of 60 K is suggested, giving densities of 20 atoms/cc and masses of 1000 MO for the absorbing clouds. (Author)