Blackett had arranged a weekend conference and this weekend conference was attended by, I think, some of the most eminent physicists in the world. At that time, Europe was becoming extremely disturbed and the refugees, both from Germany and from Italy were pouring through Blackett's department, and that was another great privilege of being in Manchester at that time. One met so many people, either in passage or they stayed for a long time and worked with Blackett.

Now, this weekend conference... I particularly remember Werner Heisenberg. Heisenberg was one of the great physicists in Germany who came from Leipzig, well-known for his uncertainty principle, and the whole of that weekend was occupied by the discussion of whether the conventional theory of high energy electrons, high energy particles was correct or whether a new particle was involved. Yukawa, a Japanese theorist had postulated that there was a heavy electron, I think then about 180 times the mass of the normal electron, which we then called a mesotron.

Well, for clarity it soon became a meson, or mason, and there are now large numbers of mesons known in particle physics, but during that weekend conference with Heisenberg believing completely in Yukawa's theory that we were studying not high energy electrons impacting on the lead plate or on the atmosphere, but one of the heavy electrons that became the matter for dispute. And gradually during that weekend I remember Blackett's view beginning to change, and before the end of the Sunday, he had been finally convinced by Heisenberg in particular and by the other physicists there that the theory was correct, and that we were dealing with a new type of particle. That may sound very odd nowadays, when there are hundreds and thousands of new particles, but one must remember that in those days we're dealing with the proton, the positive and negative electron, the neutron which had just been discovered by Chadwick. And this was remarkable, that we were adding to it a new particle which was about 180 times the area of an electron.