Philosophiae Naturalis Principia Mathematica, often also called Principia Mathematica or simply Principia, is the major work of Isaac Newton, written in Latin – so not only the church had the right to write in a language nobody from the normal people understood. No matter what, this book, although written in Latin, is one of the most influential books on physics and astronomy of all time. In this book Isaac Newton derived the law of gravity and thereby combined Galileo Galilei’s research on acceleration and Johannes Kepler’s research on planetary motion into a unified theory of gravity. Here he also introduced the concepts of absolute time, absolute space, the long-distance effect, all of which were formative for the scientific up to Albert Einstein’s theory of relativity and quantum mechanics.
Historians have assumed that only a select few scientists and mathematicians were able to comprehend the highly technical book, based on an anecdote in which a student in Cambridge said ““[T]here goes the man that writt a book that neither he nor any body else understands,”. However, anecdotes are anecdotes and do not necessarily reflect the real situation, how it was. Still, until the 1950ies only 189 copies of the first edition, published in 1687 were found. However, now – in 2020 – researchers at the University of Mannheim reported that they found about 387 copies of the first edition of the book in 27 countries, including the original 189 known ones. Most interestingly by tracking down original owners and studying the annotations that these readers made, the researchers conclude that, in addition to scientists, well-educated laypeople were reading the book, too.
Thus, the book – even though difficult to read – had a much wider audience than thought showing also that not only scientists are smart. Also, to my view, only the discussion of Newton´s ideas in this wider audience might have laid the ground for the final acceptance of his world-changing ideas.