A New System of the World

In his inaugural speech for the chair of astronomy of Gresham College in 1657, the young Christopher Wren expressed confidence that, thanks to “the industry of some writers of our age,” the foundation of Copernican astronomy, laid by Galileo and Kepler, would soon be completed and perfected. A few years later, in 1670, another Gresham professor delivered a lecture which attempted to provide an unquestionable proof of Copernican astronomy. Although unsuccessful in this respect, Hooke’s Attempt to Prove the Motion of the Earth by Observations, published in 1674, did present three new principles of the Copernican “system of the world.” The first principle introduced the idea “that all celestial bodies whatsoever, have an attraction or gravitating power towards their own centres.” This attraction is not limited to the constituents of each body, rather it extends “to all the other celestial bodies that are within the sphere of their activity.” Terrestrial gravity is part of a wider physical system, since the sun, the moon and all the other planets “have an influence” over the earth, as this latter does on them.