ABSTRACT
The whole history of science affords but few parallels to the development of astronomy from Copernicus to Isaac Newton. The progress made during that comparatively short period was so continuous and complete as to give it something of the character of a self-contained drama exhibiting the natural unfolding of the logic of events. The revolution in dynamical ideas initiated by the researches of Galileo Galilei made it necessary to formulate in new terms the problem of assigning a mechanical explanation to the motions of the planets. Galilei’s experiments showed that an external force is required, not to maintain, but to alter a body’s uniform rectilinear motion. The discovery that the Earth is flattened at the poles enabled Newton to account for the precession of the equinoxes. This phenomenon, first clearly recognized by Hipparchus, could be represented by supposing the Earth’s axis of rotation to describe a cone slowly in space.
