Letter from Thomas Gold to Dr Gordon Pettengill, Department of Earth and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts Letter of thanks on behalf of all at Cornell for the excellent job he did as Director of Arecibo Observtory. Hopes his current work does not mean the end of his association with Arecibo, and that they can look forward to tackling planetary radar with an improved upgraded instrument under his guidance. 28 December 1970