We thank the Director of the Apple ton Laboratory for the allocation of observing time;
the staff of the Appleton Laboratory and Chilbolton Observatory for maintaining the equipment;
Drs D. N. Matheson and J. A. Battilana for the installation and upkeep of the receiver during 1982 February and March;
and Drs G. H. Macdonald;
R. J. Cohen and Mr S. R. Davis for assistance with the observations. N. Matthews is indebted to the SERC for a research studentship;