谁也不知道地球会别于环绕太阳运转的其它行星。
Nobody knew that it was going to be different from other planets going round the sun.
他认为，让一颗行星在其轨道上环绕太阳运转的力量源于两种东西，一是行星和太阳的质量，二是他们之间的距离。
He decided that the strength of the force keeping a planet in orbit around the sun depended on two things. One was the amount of mass in the planet and the sun. The other was how far apart they were.
牛顿观察物体往地上落，演绎出运动原则和引力原则，并将这些原则扩展到地球的运动和环绕太阳运转的行星的运动。
Newton took the principles of motion and of gravitation as deduced from observations of earthbound objects and extended them to the motions of the earth and of the planets around the sun.
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