I believe I have a test that could shed light on fe. We know on a globe that longitudinal lines increase in distance apart from each other until they reach the equator. Then from the equator south they begin to converge, until they merge at the South Pole. If one measure two cars, say, in Australia, a mile apart, both heading due south, one could track each car to see if they are getting closer, or farther apart from each other ( you could do this with two boats just below equator) the key is each must maintain a due south course, while moving parallel to each other. This may have been done already , but I’m not aware of it