Because of the differences, British writers and their correspondents often employed two dates, dual dating, more or less automatically. For this reason, letters concerning diplomacy and international trade sometimes bore both Julian and Gregorian dates to prevent confusion: for example, Sir William Boswell writing to Sir John Coke from The Hague dated a letter "12/22 Dec. 1635". In his biography of Dr John Dee, The Queen's Conjurer, Benjamin Woolley surmises that because Dee fought unsuccessfully for England to embrace the 1583/84 date set for the change, "England remained outside the Gregorian system for a further 170 years, communications during that period customarily carrying two dates". In contrast, Thomas Jefferson, who lived at the time that the British Isles and colonies eventually converted to the Gregorian calendar, instructed that his tombstone bear his date of birth using the Julian calendar (notated O. S. for Old Style) and his date of death using the Gregorian calendar. At Jefferson's birth the difference was eleven days between the Julian and Gregorian calendars; thus his birthday of 2 April in the Julian calendar is 13 April in the Gregorian calendar. Similarly, George Washington is nowadays officially reported as having been born on 22 February 1732, rather than on 11 February 1731/32 (Julian calendar).