It was about that time that I… that I joined the group. Ryle had got it all going. He came back, I think, in late 1945 actually and was starting properly in ’46 and I joined the group in ’48. But that summer before I arrived they had discovered the radio source in… in Cassiopeia while looking at the Sun. Apparatus, as I said, was very… very primitive, but this was only part of the radio physics in… in the Cavendish, which was being run by… by Jack Ratcliffe. And most of the work in the group was ionospheric research of one sort or another, theoretical work, with people like Philip Clemmow – I don’t know if you remember him? But he had a theoretical group about the theory of plasmas and so on, and an observational group which was doing work on… on radio wave reflection from the ionosphere. And so it was Martin Ryle with about three research students and some research assistants, that was the group when I… when I arrived. And the term radio star hadn’t even been invented at that time, but… but Ratcliffe said to me, ‘Why don’t you join Ryle and have a look at these waves coming from the sky and try… try and make sense of them’. And so that’s… that’s how it was, but it was only a small part of the… of the ionospheric group. But because Ratcliffe himself wasn’t technically involved with the… with the first radio telescopes, it was Martin Ryle who was doing everything himself with… with help, the radio … astronomers were left to themselves to get on and… and Ratcliffe gave them as much support as… as he could. And I mean, it was extremely hands-on work because Ryle didn’t want to waste any money – well, we didn’t have any money to waste – and everything was done by ourselves.

And my first job as a graduate student, which surprised me rather, having just spent my… my 2 post-war years finishing off the degree, to be told, look, there’s a pile of brass tubing there, we want that cut up into dipoles, you’ll find a hacksaw in the workshop, go and make a dipole array for me. And I mean, I spent my first summer doing… doing that. And we got used to doing all these hard mechanical jobs ourselves, and I mean I can remember cycling out to the… to the site here in Cambridge with…with dipoles across my handlebars; you know, that’s… that’s the sort of life that it… that it was. But then we built the first arrays and began to see that the sky was filled with these so-called radio stars and then Martin Ryle thought they were stars like our Sun but more distant, within our galaxy. And he was convinced that all these things were… were part of our galaxy, but it was only later in… in the early 1950s when Graham Smith, using wartime Wurzburg antennas, was able to fix the positions of four of them with sufficient accuracy to send the positions off to the astronomers in California. The 200-inch optical telescope at Palomar was then the most powerful instrument in the world. And they looked at these… some of these positions and because Graham Smith had fixed the error bars to such tight limits, they were able to identify, in particular Cygnus A, which turned out to be a galaxy just on the very limit of detection with a 200-inch telescope. And that’s,  I think, when the full potential of radio astronomy actually burst upon us because here were we with the very crude instruments, essentially, knocked up over… over a month, over a few months almost, able to locate astronomical objects which you could only just reach with the most powerful optical telescope that existed. And so it was immediately clear then that these were, at least some of them, were distant galaxies on the… on the very edges of the universe as it… as it was then known. And the full potential of the… of the field became evident and Martin Ryle, in particular, was interested in the… in the origin of the universe, once he got over the shock of discovering that these things he was looking at, many of them were not in our own galaxy. Some of them were, of course, supernova remnants like the Crab Nebula. They… that, I think, was first identified by the Australians actually, which was a group in Sydney run by Joe Pawsey, which was very like Martin Ryle’s group. It was ex-wartime scientists coming back looking for something to do and they had the radar gear at their… at their disposal, as it were. And Joe Pawsey’s group had their cliff interferometer, they… they used waves reflected off the sea. They had an antenna mounted along the cliff top and had a simple interferometer working on reflection from the ocean. But the idea that you could get angular resolution by using the Michelson interferometer principle, which was nothing to do with radio astronomy, as… – I mean, that was an optical invention – that was applied immediately and then… then the whole field began to open up. And then Martin Ryle became… I mean, the radio astronomy part of the… of the ionospheric group began to outweigh the ionospheric part because it was much more exciting and growing rapidly. And Ratcliffe was… although he was nominally Head of Radio Physics, he… he gave Martin his own reins and backed him fully and helped, in fact, to… eventually, to establish the Mullard [Radio Astronomy] Observatory, to which we later moved.