  Although Newton obviously had far less time available to devote to solitary research during his London years than he had had in Cambridge, he did not entirely cease to be productive. The first (English) edition of his Opticks finally appeared in 1704, appended to which were two mathematical treatises, his first work on the calculus to appear in print. This edition was followed by a Latin edition in 1706 and a second English edition in 1717, each containing important Queries on key topics in natural philosophy beyond those in its predecessor. Other earlier work in mathematics began to appear in print, including a work on algebra, Arithmetica Universalis, in 1707 and “De Analysi” and a tract on finite differences, “Methodis differentialis” in 1711. The second edition of the Principia, on which Newton had begun work at the age of 66 in 1709, was published in 1713, with a third edition in 1726. Though the original plan for a radical restructuring had long been abandoned, the fact that virtually every page of the Principia received some modifications in the second edition shows how carefully Newton, often prodded by his editor Roger Cotes, reconsidered everything in it; and important parts were substantially rewritten not only in response to Continental criticisms, but also because of new data, including data from experiments on resistance forces carried out in London.  Focused effort on the third edition began in 1723, when Newton was 80 years old, and while the revisions are far less extensive than in the second edition, it does contain substantive additions and modfications, and it surely has claim to being the edition that represents his most considered views.