The visibility functions of 195 radio sources are interpreted in terms of the structure of these -sources. Of the 195 sources, 174 are known or presumed to be extragalactic. Seventy-five of these extragalactic sources are resolved with the interferometer spacings used, and complex structure is found i n all but 13. In the sources showing complex structure, two similar components with nearly equal intensities are found in 15, 40 show two or more components of unequal intensities, while 7 appear to be a bright core surrounded -by a halo.
The intensity variations in radio source 3C 273B have been measured at wavelengths of 31.3, 21.2, and 10.6 centimeters. At 31.3 centimeters the variation is quite small, indicating that the variable component of the source is optically thick at this wavelength. Study of several dijfferent model sources shows that the observed dependence of the intensity variations on frequency can best be explained by an increase of the electron density in a source region about 2 parsecs in diameter. This interpretation is consistent with the distance to 3C 273 determined from Hubble's law and the observed red shift.
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