The Mathematical Principles of Natural Philosophy, Book III: Of the System of the World
Phænomenon VI
That the moon, by a radius drawn to the earth’s centre, describes an area proportional to the time of description.
This we gather from the apparent motion of the moon, compared with its apparent diameter. It is true that the motion of the moon is a little disturbed by the action of the sun: but in laying down these Phænomena I neglect those small and inconsiderable errors.