He was the son of a nonconformist minister, and was born at Wood Eaton in Oxfordshire, 5 March 1625. Apprenticed at the age of sixteen to Thomas Allam, a bookseller, living outside the Turl Gate of Oxford, he was driven to quit the trade by the troubles of the time, and accepted a clerkship in the employment of John Marr, clerk of the kitchen to the Prince of Wales. From him he derived some instruction in mathematics, but the outbreak of the First English Civil War drove him to sea for seven years, 1642-9, most of which time he spent on board an English merchantman, engaged by the Venetians as a ship of war in their defence of Candia against the Turks.