Numerical experiments on three-dimensional convection in the presence of an externally imposed magnetic field reveal a range of behaviour that can be compared with that observed at the surface of the Sun (and therefore expected to be present in other similar stars). In a strongly stratified compressible layer small-scale convection gives way to a regime with flux separation as the field strength is reduced; with a weak mean field magnetic flux is concentrated into narrow lanes enclosing vigorously convecting plumes. Small-scale dynamos, generating disordered magnetic fields, have been found in Boussinesq calculations with very high magnetic Reynolds numbers; there is a gradual transition from dynamo action to magnetoconvection as the strength of the imposed field is increased.

Introduction

Thirty-seven years ago, when I was a postdoc at Culham, Roger Tayler told me that he was sending a very bright young research student to spend the summer there – and so I first met Douglas. When I moved to Cambridge a year later he was finishing his Ph.D. and then he and Rosanne went off to the States for a few years. We've been in close contact ever since they returned to Cambridge and it has been a great pleasure having Douglas as a colleague and a friend – always stimulating and often argumentative, but never causing any serious disagreement. So I am very glad to have a chance of saying ‘Thank you’ here.

As we have already been reminded, Douglas's third paper (Gough & Tayler 1966) was on magnetoconvection.