I love the back story to this:

“Much of Newton’s important work on calculus is developed in this large notebook, which he began using in 1664 when he was away from Cambridge due to the plague. Newton inherited the book from his stepfather, Rev Barnabas Smith, who used it from about 1612 to record his own theological notes (see, for example, his notes on adultery, in Latin). Newton was not interested in his stepfather’s jottings: its value to him was the large number of blank pages, which he began filling with his mathematical and optical calculations. Although the bulk of his work in this manuscript dates from the mid-1660s, Newton continued to use into the 1680s and possibly even the 1690s.” (link)

More of Newton’s papers at the Cambridge Digital Library