Referee's report by John Turton Randall, on a paper 'The inversion spectrum of ammonia at centimetre wave-lengths' by Brebis Bleaney and R P Penrose Sectional committee: Physics Recommended for publication in Proceedings. It is an 'elegant piece of work', which is clear and concise. The author's attention should be drawn to other recently published work on the same subject by Good and Hershberger. The possibilities and difficulties in using the technique should be described. Letter states that the authors have dealt with his previous points and the paper is now ready for publication. [Published in Proceedings of the Royal Society A, 1947]. Letter endorsed on recto as received 16 October 1946. 1946