ALTHOUGH he has held the Plummer chair of theoretical chemistry in the University of Cambridge for fourteen years, only for about one half of that time has Sir John Lennard-Jones been the academic man pure and simple. Since early in the War he has been a Government servant ; and his resignation from the post of Director General of Scientific Research (Defence) has just been announced. Sir John first left his university post, to which he is now returning, in 1939, when he joined the Ministry of Supply to take charge of a group of scientific workers. Later, as chief superintendent of armament research, he controlled research being done for all three Fighting Services. His wide experience in the armaments field goes back to the First World War, when he left the R.F.C. as a flying officer to work at the Experimental Station at Orfordness. Latterly, as Director-General of Defence Research, he was in charge of a dozen stations scattered the length and breadth of Britain. Although he is now going back to Cambridge, Sir John will still be connected with the Ministry of Supply, the University having agreed to make his services available on a part-time basis chief scientific adviser.