It's a sad fact that after all these years I can't remember if it was Champion or Chapman who regailed us with his war-time exploits using microwave radiation and the fact that on cold nights they would cook potatoes in their appartus while they waited for the next wave of Luftwaffe planes.

Nigel Wood found this fragment on the web. This is Rudolph Peierls, back in the 1960s, recalling his experiences from the 1920s and 1930s...

There was one physicist then I think in Cambridge, Champion, who was investigating beta decays with a cloud chamber. He took thousands of photographs of beta ray tracks in a cloud chamber, sometimes with and sometimes without a magnetic field. He used various sources, some of which give positrons and some of which don't. He had no actual positron emitters, but sometimes you have a mixed decay, or sometimes you have a secondary positron through a pair creation by gamma rays, and so on. And it so happened that he never had a magnetic field on with any sources which contained positrons. I mean, many of his tracks must in fact be positrons. Almost any source gives you, if the energy is high enough, some positrons, but of course if you see one or two tracks of the wrong curvature, then you think there are secondary particles going the other way. He must have felt rather bad after the discovery of the positron because if he'd just happened to have a magnetic field on, on the right occasion, he would have seen lots of them, well before they were discovered.

This must be his? University Physics

And this? Champion & Davy