Published online by Cambridge University Press: 14 August 2015
I should like to open my subject by attempting to answer the following question: how many parameters are necessary and sufficient for a complete specification of the form of both components in close binary systems? Their shape should, in principle, be specified by the nature of forces acting on their surfaces, and (provided that the free period non-radial oscillations of both components are short in comparison with that of their orbits) their distortion should be governed by the equilibrium theory of tides. The level surfaces of constant density then coincide with those of constant potential, and the boundary of zero density becomes a particular case of such equipotentials.