Isaac Newton (1642–1727) is best known for having invented the calculus in the mid to late 1660s (most of a decade before Leibniz did so independently, and ultimately more influentially) and for having formulated the theory of universal gravity — the latter in his Principia, the single most important work in the transformation of early modern natural philosophy into modern physical science. Yet he also made major discoveries in optics beginning in the mid-1660s and reaching across four decades; and during the course of his 60 years of intense intellectual activity he put no less effort into chemical and alchemical research and into theology and biblical studies than he put into mathematics and physics. He became a dominant figure in Britain almost immediately following publication of his Principia in 1687, with the consequence that “Newtonianism” of one form or another had become firmly rooted there within the first decade of the eighteenth century. His influence on the continent, however, was delayed by the strong opposition to his theory of gravity expressed by such leading figures as Christiaan Huygens and Leibniz, both of whom saw the theory as invoking an occult power of action at a distance in the absence of Newton's having proposed a contact mechanism by means of which forces of gravity could act. As the promise of the theory of gravity became increasingly substantiated, starting in the late 1730s but especially during the 1740s and 1750s, Newton became an equally dominant figure on the continent, and “Newtonianism,” though perhaps in more guarded forms, flourished there as well. What physics textbooks now refer to as “Newtonian mechanics” and “Newtonian science” consists mostly of results achieved on the continent between 1740 and 1800.
Newton's life naturally divides into four parts: the years before he entered Trinity College, Cambridge in 1661; his years in Cambridge before the Principia was published in 1687; a period of almost a decade immediately following this publication, marked by the renown it brought him and his increasing disenchantment with Cambridge; and his final three decades in London, for most of which he was Master of the Mint. While he remained intellectually active during his years in London, his legendary advances date almost entirely from his years in Cambridge. Nevertheless, save for his optical papers of the early 1670s and the first edition of the Principia, all his works published before he died fell within his years in London.
Three factors stand in the way of giving an account of Newton's work and influence. First is the contrast between the public Newton, consisting of publications in his lifetime and in the decade or two following his death, and the private Newton, consisting of his unpublished work in math and physics, his efforts in chymistry — that is, the 17th century blend of alchemy and chemistry — and his writings in radical theology — material that has become public mostly since World War II. Only the public Newton influenced the eighteenth and early nineteenth centuries, yet any account of Newton himself confined to this material can at best be only fragmentary. Second is the contrast, often shocking, between the actual content of Newton's public writings and the positions attributed to him by others, including most importantly his popularizers. The term “Newtonian” refers to several different intellectual strands unfolding in the eighteenth century, some of them tied more closely to Voltaire, Pemberton, and Maclaurin — or for that matter to those who saw themselves as extending his work, such as Clairaut, Euler, d'Alembert, Lagrange, and Laplace — than to Newton himself. Third is the contrast between the enormous range of subjects to which Newton devoted his full concentration at one time or another during the 60 years of his intellectual career — mathematics, optics, mechanics, astronomy, experimental chemistry, alchemy, and theology — and the remarkably little information we have about what drove him or his sense of himself. Biographers and analysts who try to piece together a unified picture of Newton and his intellectual endeavors often end up telling us almost as much about themselves as about Newton.
