Is solar activity related to magnetic buoyancy? This possibility has been considered recently by solar physicist John H. Thomas of the University of Rochester (Nature, 280, 622–663, 1979) in analyzing the effects of the solar dynamo on variations of the sun's radius and temperature. The solar luminosity is given by L = 4πRS2 σ T4 where RS is the solar radius, and thus a decrease in temperature T could imply radial expansion rather than reduction in luminosity L, as has been suggested. A drop in surface temperature of 1°K could be interpreted as a relative radial increase or expansion of ΔRS/RS ∼ 3 x 104.