 De Moivre continued his studies of mathematics after visiting the Earl of Devonshire and seeing Newton's recent book, "Principia Mathematica".Looking through the book, he realised that it was far deeper than the books that he had studied previously, and he became determined to read and understand it.However, as he was required to take extended walks around London to travel between his students, de Moivre had little time for study, so he tore pages from the book and carried them around in his pocket to read between lessons.