This meeting took place. By the afternoon François had come to my house in Cambridge, and we had designed the nature of the experiment that was later to be produced; that is, we realise we have to show… have to show that this new RNA is on old ribosomes and we… I realised very immediately that this could only be done on bacteriophage where we have the switch from old to new synthesis. And how would we tell the difference between old and new? Well, we would do it by the tricks developed by Meselson and Stahl which had… they'd developed for DNA. Namely we would label these with heavy isotopes – that is with Carbon 13, Nitrogen 15 – and we would be able by density gradient centrifugation just to weigh them and discover whether they were old or new, and that's one thing to say all of that and another thing to do it. Of course, the people who had all the amino acids made with the heavy isotopes were in California – that was Matt Meselson. I had learnt that François was going to go to California that summer, had been invited there, and what had happened was that I had been invited to come to California – another reason, and so we fixed it that we would go and do this experiment in California in... in the following June; it's a couple of months, and I fixed it with Matt Meselson we'd be able to use his isotopes and his equipment.