New limits to the diameters of some radio sources

THE investigations at Jodrell Bank of the angular diameters of extra-terrestrial radio sources have now reached the stage where interferometric observations are being made with a base-line of 32,000 wavelengths. The interferometer operates at a wavelength of 1.89 m., and uses the 250-ft. steerable paraboloid in conjunction with auxiliary aerials which are now placed about 40 miles to the west of Jodrell Bank near the Welsh coast. This is the longest baseline to be used so far for the observation of radio sources, and it is possible with this instrument to set new limits to the diameter of some radio sources which are significantly smaller than those previously reported¹.