Untitled talk, Los Alamos, New Mexico, USA, April 1981, R H Brown Handwritten outline, two slightly different copies. Presented also at the Very Large Array facility, Socorro, New Mexico, USA, April 1981; the National Radio Astronomy Observatory, Charlottesville, Virginia, USA, 2 May 1983; the European Southern Observatory, Garching near Munich, Germany, September 1983; and the Rutherford-Appleton Laboratory, Oxfordshire, July 1984. 1981