The central university library at Cambridge, in the United Kingdom, is an imposing, towered building known affectionately for being called a “magnificent erection” by, before he became prime minister, Neville Chamberlain.^{1} When I was a graduate student there, studying astronomy, rumors circulated within my cohort that if you went to the library and asked nicely, you would be allowed to examine, under supervision, a first edition of Isaac Newton’s *Principia*, first published in 1687, complete with his own handwritten notes in the margins and inserted sheets.

All of which suggested a marvelous adventure. The *Principia*, or *Philosophae Naturalis Principia Mathematica* (*Mathematical Principles of Natural Philosophy*), has a mythological status. It was in fact three books: the first two covering the propositions and laws of motion, along with the innate attraction of all bodies to each other (gravitation), and the third being *On the system of the world*, in which Newton applied all of his insights to the detailed motions of the planets and their satellites, including our moon, the tidal motions, and even comets. These books laid out the quantitative foundations of classical mechanics, established the idea of gravity as a force sculpting the cosmos, and set up space and time as absolutes.