isosurface { //-------------------------------------------------------------
  function{
     f_spiral(
        x,y,z,
        0.2,  // distance between windings,
        0.05, // thickness,
        0.9,  // outer diameter of the spiral,
        0,    // not used,
        0,    // not used,
        0.75   // cross section type
     )
  }          
 contained_by {sphere {<0,0,0>,1}}
 threshold 0
 max_gradient 5
 
 texture{ pigment{ color rgb <1,0.75,0.00>} 
          //normal { bumps 0.15 scale 0.015}
          finish { specular 0.2 phong 0.7 }
        }
 rotate<90,0,0>
 scale 1.25
 translate< 0,1.2,0>
} // end of isosurface -------------------------------------------------------