It is always cool to repeat classic experiments. How many of us know the radius of the Earth because we determined it on our own? I haven't done this, at least not yet. For all my life I have just ...

I don't know where he got this idea (surely not from the internet), but Eratosthenes estimated the radius of the Earth by looking at two shadows at two different locations on the Earth. This diagram ...

IN a paper entitled "The Story of Newton's Inverse Square Law and his Use of a False Radius of the Earth" (J. Brit. Astro. Assoc., 50, 2; 1939), John Miller states that the story of Newton's alleged ...