I came to the conclusion, I spent so much time making the X-ray tube at Oxford work, it would be better to go  somewhere else where they had all the apparatus and knew more what to do than Tiny and Professor Bowman at that moment, and so I reverted to these advisers who suggested WH Bragg, and there was one other who was Lowry, Professor of Physical Chemistry in Cambridge, who said, we have a very good young man here, Bernal, who we've just appointed to start X-ray analysis going in Cambridge; why not send her here? And, the moment this idea floated round, it somehow took, because Bernal at that moment published the first notes of his measurements of the sterols, on a group of sterols, and they were very revolutionary, and obviously a biochemical subject of great interest, which...

[Q] Yes. It's also chemically very difficult?

Yes. So, so I went to Cambridge, and took photographs for Bernal on all the different things that came in, which were really all the things that the serious chemists, the organic chemists, were working on at the moment, such as the different derivatives of the sterols, and the sex hormones, testosterone, oestrone, and vitamin B1, hypochlorite, and I took the X-ray photographs and measured the densities of the crystals and determined the molecular weights. And, but all that I was thinking, really, was to settle down and work on one of these compounds, but I never did get round to doing it in Cambridge. But when I got offered an appointment at Oxford, at Somerville College, to do teaching and some research, I thought I will take some of Bernal's crystals with me, and work on one of them. It was a lucky moment in history, because, just at that moment, Patterson had discovered the Patterson [map] and published it, so there was a way to begin to look at crystals and find out something about them which hadn't been possible before. And I, I took cholesterol iodide with me in one bottle, and cholesterol bromide and chloride, because, well, the... it seemed desirable to have a heavy atom somewhere in the crystal to provide guidance to the phase constance of the structure factors.