# History of Newtons law of gravitation

I have some questions about the history of Newtons law of universal gravitation.

1. Did Newton discover his three laws of motion before he discovered the universal law of gravitation?

2. I know two versions of how he discovered it. The first one is that he applied Keplers laws to derive it. The second one is that he considered the motion of the moon compared to an imaginary cannon ball going around the earth. More precisely he compared the centripetal accelerations of the two (assuming that the orbit of the moon is circular). Knowing the radius $r_E$ of the earth and that the distance of moon earth is roughly $60 \cdot r_E$ he derived that the centripetal acceleration of the moon is $3600 = 60^2$ times smaller than that of the cannon ball ($g = 9,81\,\mathrm{\frac{m}{s}}$). Thus he guessed the $\frac{1}{r^2}$ dependency. With his second and third law he also established the proportionality to the masses of moon and earth. I think he already tried this 15 years but didn't succeed because the radius of the earth was not known precisely enough. A third version I know is that at first he did the second derivation and after that he also did it using Keplers laws.

It would be great if someone could bring all this into the correct history order and give more details and dates about the history of the discovery of the universal law of gravitation. I am also looking for good references about this.

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–  Ben Crowell Jun 13 '13 at 21:39
This is only related to what you ask, in case you do not already know. Thomas Kuhn's dissertation on the Copernician Revolution is a classic and reads like some SciFi novels, –  babou Jun 13 '13 at 22:33