Let me close by reminding you of what Newton actually did on the day that he conceived <math>G = k \frac{mm'}{r^2}</math>. ...Newton did not have any… - Jacob Bronowski

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Let me close by reminding you of what Newton actually did on the day that he conceived <math>G = k \frac{mm'}{r^2}</math>. ...Newton did not have any subsidies, grants, funds, Secret Service money. But he had the moon. He said, "... I cannot throw a ball round the world, but let me picture the moon as if it were a ball which has been flung around the world... How long will it take to go round the world?" ...He knew the value of gravity at the earth's surface ...but he did not know the value of the earth's gravity for the moon. He said, "Let us suppose that it is given by an inverse square law. Now, how long will it take the moon to go around?" It comes out at twenty-eight days. As Newton said, "They agreed pretty nearly."