August 2011, page 80—The photograph was taken by Eric Brown.

September 2011, pages 44, 46—In box 2, the first of the Boussinesq equations should be

and the Rayleigh number should be RagαL3ΔT/κν. In the text on page 46 the Ekman number should be Eν(2ΩL2)−1. We thank Paul Asimow for pointing these out.