We thank the Director of the Appleton Laboratories for affording us time with the Chilbolton telescope;
the staff of the Appleton Laboratories and the Chilbolton Observatory for maintaining the equipment;
Drs D. N. Matheson and T. Battilana for their efforts in installing the water line receiver at Chilbolton;
and the staff of the UK Infrared telescope for their assistance. ATB and NM are indebted to SERC for research studentships;