General formulas are derived which specify the heat flux over an arbitrary receiving surface for radiation incident upon and specularly reflected from an arbitrary curved surface. The direction of the reflected ray and its intersection with the receiving area provides a transformation which maps an element of reflecting area onto the receiving area through the Jacobian determinant. Results are expressed in terms of the equations of the surfaces. The general formulas are reduced to the special case for which the reflecting area is a surface of revolution. © 1973.