I also went up to Sheffield where there were some experiments on the fast cooling of steel and the austentite-pearlite transformation, which... which I interpreted, they were doing rods. It turned out that [Douglas] Hartree had done a great... major contribution to the war effort because he discovered in trying to account for this phase transformation by a very primitive method using a heat... a temperature dependent diffusion coefficient. He had found that the cooling of steel ingots in Sheffield they used to take their steel, the hot ingots, quench them and leave them for nine hours overnight to make sure transformation of steel was complete. He was... he worked out it was complete in four hours, so they actually doubled the production, rate of production.

[Q] Yeah.

Just sort of... so, it was really a reflection on British industry. No attempt at all to try to do anything scientific, a way to find out, they could have at least. So Hartree got them to make small ingots, little cylindrical bars and measure temperatures inside and out and follow the process. So what he wanted to know was what was going on, so I developed a model, I made a kind of armed raid on metallurgy and there was quite a lot known about steel, austentite-pearlite transformation... transition. And so I developed a model, which the new phase nucleated, and I could... that's the function of the under-cooling past the transition temperature and the dissipation of the heat. So I developed a nucleation and growth model, that's what I called it. And I was able to account very well for the... for the characteristics of the cooling; people used that in some other phase transformations later.

[Q] Phase changes were followed by X-rays weren't they?

No, no, purely measuring temperature because as you went through the... as you went through the transition the temperature stayed pretty constant, pretty flat because you were dissipating the latent heat.

[Q] Yes.

And so and now the point I mention is that later when I came to work on the assembly of Tobacco Mosaic Virus, I realised it had to be divided into nucleation and growth. And the nucleating... the... well, I'll come to that, but the... it was that, I must have had it in my mind although I don't remember doing it consciously. But when I came to the assembly of Tobacco Mosaic Virus it was a disc of... a disc of Tobacco Mosaic Virus would act as the nucleating agent for the assembly. And that's what led to those classic experiments where we could now grow Tobacco Mosaic Virus in six minutes rather than 24 hours.

[Q] Yes.

So... so it shows you that... you never need to know what you need to know because it's... it's chance, it's these things are very... it's all... chance, I guess I would have done something else.