The surface of a revolution of a circle with the radius $b$ about a line in the plane of the circle at a distance $a$ from the centre of the circle is called a torus, spire or ring surface; this is an algebraic surface of the fourth degree with the equation

" (x^2 + y^2 + z^2 + a^2 - b^2) = 4a^2(x^2 + y^2) "

in a suitably chosen Cartesian coordinate system. We know three types of ring surfaces: a) $a>b$ an open torus, b) $a"