[drbaskin]

I don't know whether this is the Lorenz they are referring to, but there was another Lorenz who worked in optics. http://en.wikipedia.org/wiki/Ludvig_Lorenz

In fact, there is a Lorentz-Lorenz equation. Somewhat more confusingly, when you study Maxwell's equations on a Lorentz background, it is often convenient to work in the Lorenz gauge.