Suppose an experimenter firstly is entirely ignorant of general relativity and non-euclidean space. He finds (say) a point-source gravitational field. He fires light beams about and notices the deflection. He concludes that there's a not-equals-one index of refraction n about the source point. Let's say he is able to recognize and make a formula for n with no problems. What is the function n( r ) ? SURELY this has been formulated! Does anyone have this formula?