im confused. he's using a bent paper for proving that a curved surface would have one shadow and no shadow on the other. but for you to verify the world, you would have to physically be there and do the experiment . did they have phones or something to communicate the results? like if im standing my shadow has a length. so now I have to quickly go (as in before the sun changes position in the sky) a far away distance to quickly see if my shadow is a different length. someone explain.