Before NASA there was NACA, the National Advisory Committee on Aeronautics. NACA was upgraded into NASA in 1958 – shortly after the then USSR launched the first satellite, Sputnik, and the USA decided they needed to pull their finger out in space. Anyway, back to NACA. In the late 1940s NACA worked with the US Air Force and Bell to make the X-1 – the first plane to exceed the speed of sound (without diving).

As well as flying faster than any plane had done before, the X-1 also flew higher than any plane before, up to 27 km up. It is very cold up there, and NACA worried about ice forming on planes if they flew through supercooled clouds. A supercooled cloud is a cloud of liquid droplets that are below 0C.

Droplets, especially in the clean conditions in the upper atmosphere, can often cool down to well below 0C. Water does not freeze at 0C, it is much more complex than that.  But in a supercooled cloud at some point the droplets will freeze, and NACA was worried they would freeze on a plane, endangering it.

So they did some experiments, and  then a NACA employee, Joseph Levine, developed a model. This was in 1950, and it has led to a whole series of daughter models, running down to the present day. The fun thing, at least if you interested in the weird way science can sometimes work, is that only two years later, in 1952, another scientist, a smart guy called David Turnbull, realised that Levine was using what mathematicians call ‘extreme-value statistics’. But the scientists who followed on from Levine somehow did not grasp Turnbull’s observation, or its implication that results statisticians had developed could be applied to the freezing of droplets.

Then I came along 60 years after Turnbull, and independently developed some results using extreme-value statistics. At the time I did not know  that Turnbull had seen the link back in the 1950s.

I only read Levine’s and Turnbull’s papers recently. When I did, it was a bit weird but also kind of exciting to see that part of what I had done had been scooped over 60 years ago. You feel a connection to these scientists working 60 years ago. We have a lot in common, we looked at very similar problems, and basically had the same solution.