We have seen that the relative movement of a conducting body and a magnetic field can lead to the dissipation of energy. This has been used by engineers for over a century to dampen unwanted motion. Indeed, as far back as 1873 we find Maxwell noting: ‘A metallic circuit, called a damper, is sometimes placed near a magnet for the express purpose of damping or deadening its vibrations.’ Maxwell was talking about a magnetic field moving through a stationary conductor. We are interested in a moving conductor in a stationary field, but of course, this is really the same thing. We have already touched upon magnetic damping in Chapter 5, and we discussed some of its consequences in Chapter 6. In particular, we saw that the intense magnetic field in a sunspot locally deadens the convective motions in the outer layer of the sun, thus cooling the spot and giving it a dark appearance. Here we make the jump from sunspots to steelmaking, and describe how magnetic fields are used in certain casting operations to suppress unwanted motion.

There has been a myriad of papers on this topic and at times one is reminded of Rayleigh's indigestion. Here we focus on the unifying themes.