In 1686 Halley proposed that a heat source moving over a layer of fluid would induce an average horizontal flow. Recent work on this problem is reviewed and related to the literature on Hadley cells. An Oseen-type solution is constructed for the composite nonlinear problem. The application of this solution to the atmosphere of Venus determines a value for the zonal flow in keeping with the observed circulation of the visible clouds. This is possible because the theoretical maximum velocity depends only very weakly on the atmospheric mixing processes. Other aspects of the theory relate potential observables, such as the solar-antisolar temperature contrast and the depth of the high-velocity region, to the unknown magnitudes of the turbulent transport of heat and momentum.