[Footnote 369: One London bookseller in 1670 advertised for sale "spheres according to the Ptolmean, Tychonean and Copernican systems with books for their use." (Moxon: 272.) In 1683 in London appeared the third edition of Gassendi's _Institutio_, the textbook of astronomy in the universities during this period of uncertainty. It too wavers between the Tychonic and the Copernican systems.] The appearance of Newton's _Principia_ in 1687 with his statement of the universal application of the law of gravitation, soon ended hesitancy for most people. Twelve years later, John Keill, (1671-1721), the Scotch mathematician and astronomer at Oxford, refuted Descartes's theory of vortices and opened the first course of lectures delivered at Oxford on the new Newtonian philosophy.[370] Not only were his lectures thronged, but his books advocating the Copernican system in full[371] went through several editions in relatively few years. [Footnote 370: _Dict. of Nat. Biog._: "Keill."] [Footnote 371: Keill: _Introductio ad Veram Astronomiam_.] In the Colonies, Yale University which had hitherto been using Gassendi's textbook, adopted the Newtonian ideas a few years later, partly through the gift to the university of some books by Sir Isaac himself, and partly through the enthusiasm of two young instructors there, Johnson and Brown, who in 1714-1722 widened the mathematical course by including the new theories.[372] The text they used was by Rohault, a Cartesian, edited by Samuel Clarke with critical notes exposing the fallacies of Cartesianism. This "disguised Newtonian treatise" was used at Yale till 1744. The University of Pennsylvania used this same text book even later.[373] [Footnote 372: Cajori: 29-30.] [Footnote 373: Cajori: 37.] In 1710 Pope (1688-1744) refers to "our Copernican system,"[374] and Addison (1671-1719) in the _Spectator_ (July 2, 1711) writes this very modern passage: