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“There goes the man that writt a book that neither he nor any body else understands.”

So declared a Cambridge University student as Isaac Newton passed him on the street. And the book that Newton “writt” was his monumental work on physics, Philosophiæ Naturalis Principia Mathematica (The Mathematical Principles of Natural Philosophy), better known as Newton’s Principia. Thanks to the volunteers at Distributed Proofreaders and Project Gutenberg, you can delve into an English translation of this major milestone of science for free.

In a letter to fellow physicist (and bitter rival) Robert Hooke, Newton famously said, “If I have seen further it is by standing on the shoulders of giants.” The Principia is the work of a giant. In it, Newton expounds, with mathematical proof, what is now the bedrock of modern physics: his groundbreaking laws of motion and universal gravitation, and his explanations of the motion of planets, moons, comets, tides, fluids, and other physical phenomena.

The Principia arose from a dispute among Hooke, the astronomer Edmond Halley, and the architect Christopher Wren about using mathematical derivations to demonstrate Kepler’s laws of planetary motion. Halley visited Newton at Cambridge in 1684 to discuss the question and was astonished to learn that Newton had already worked out the derivations. A few months later, Newton sent Halley a nine-page paper on the subject, De motu corporum in gyrum (Of the Movement of Bodies in Orbit). Halley, thunderstruck by what he perceived as a revolution in celestial mechanics, urged the Royal Society to publish it. But Newton wanted to rework it first. For the next two years, Newton obsessively expanded his paper, often forgetting to eat. The nine-page manuscript turned into a three-volume book – in Latin, the scientific language of the day – and was finally published in 1687, under the imprimatur of the great diarist Samuel Pepys, then the President of the Royal Society. (The English version at Project Gutenberg is the first American edition of 1846, using British mathematician Andrew Motte’s 1729 translation; the original Latin version was also prepared for Project Gutenberg by Distributed Proofreaders volunteers.)

The publication of the Principia transformed Newton’s life and career. Though he was a distinguished professor at Cambridge who had spent years in dogged research and experimentation in mathematics, mechanics, dynamics, optics, and even alchemy, he had never actually completed any of this work. Now, in his 40s, he had finally brought forth his highest accomplishment, a work that, though he could not have foreseen it then, ultimately enabled human beings to leave Earth to explore the universe beyond it. It was an instant hit throughout Europe among mathematicians, physicists, and even philosophers like John Locke, who did not understand the math but very much appreciated the scientific principles. Hooke was so impressed that he claimed Newton had stolen the ideas from him, but no one ever believed him.

Preparing the e-book version of the Principia posed quite a few challenges, including dealing with numerous mathematical equations and symbols, diagrams, tables, Greek letters, and astrological symbols. Many Distributed Proofreaders volunteers worked hard on it over the years to make this historic work freely accessible to all.

This blog post was contributed by Linda Cantoni, a Distributed Proofreaders volunteer, and is dedicated to the memory of Chris Curnow and John Welch, beloved Distributed Proofreaders volunteers who helped prepare Newton’s Principia.