John Wallis was appointed Savilian Professor of Geometry at Oxford University in 1649. He was then a relative newcomer to mathematics, and largely self-taught, but in his first few years at Oxford he produced his two most significant works: De sectionibus conicis and Arithmetica infinitorum. In both books, Wallis drew on ideas originally developed in France, Italy, and the Netherlands: analytic geometry and the method of indivisibles. He handled them in his own way, and the resulting method of quadrature, based on the summation of indivisible or infinitesimal quantities, was a crucial step towards the development of a fully fledged integral calculus some ten years later.

To the modern reader, the Arithmetica Infinitorum reveals much that is of historical and mathematical interest, not least the mid seventeenth-century tension between classical geometry on the one hand, and arithmetic and algebra on the other. Newton was to take up Wallis's work and transform it into mathematics that has become part of the mainstream, but in Wallis's text we see what we think of as modern mathematics still struggling to emerge. It is this sense of watching new and significant ideas force their way slowly and sometimes painfully into existence that makes the Arithmetica Infinitorum such a relevant text even now for students and historians of mathematics alike.

Dr J.A. Stedall is a Junior Research Fellow at Queen's University. She has written a number of papers exploring the history of algebra, particularly the algebra of the sixteenth and seventeenth centuries. Her two previous books, A Discourse Concerning Algebra: English Algebra to 1685 (2002) and The Greate Invention of Algebra: Thomas Harriot's Treatise on Equations (2003), were both published by Oxford University Press.

To the most Distinguished and Worthy gentleman and most Skilled Mathematician, Dr William Oughtred, Rector of the church of Aldbury in the Country of Surrey.- To the Most Respected Gentleman Doctor William Oughtred, most widely famed amongst mathematicians, by John Wallis, Savilian Professor of Geometry at Oxford.- Doctor William Oughtred: A Response to the preceding letter (after the book went to press). In which he makes it known what he thought of that method.- The Arithmetic of Infinitesimals or a New Method of Inquiring into the Quadrature of Curves, and other more difficult mathematical problems.