Beginning in 1582, the Gregorian calendar replaced the Julian in Roman Catholic countries.
This change was implemented subsequently in Protestant and Orthodox countries, usually at much later dates.
The need for change arose from the realisation that the correct figure for number of days in a year is not 365.25 (365 days 6 hours) as supposed by the Julian calendar but almost exactly 365.2425 days (365 days 5 hours 49 minutes 12 seconds), a reduction of 10 minutes 48 seconds per year: the Julian calendar has too many leap years. When this usage is encountered, the reader should not assume that the British adoption date is intended, or that the 'start of year' change and the calendar system change were adopted concurrently, or even that religious adoption accompanied civil adoption.
Because of the differences, English people and their correspondents often employed two dates, dual dating, more or less automatically.
Events in continental western Europe are usually reported in English language histories as happening under the Gregorian calendar.
For example, the Battle of Blenheim is always given as 13 August 1704.
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co.
This article is about the 18th-century changes in calendar conventions used by Great Britain and its colonies, together with a brief explanation of usage of the term in other contexts. S.) are terms sometimes used with dates to indicate that the calendar convention used at the time described is different from that in use at the time the document was being written.
Claims that rioters demanded "Give us our eleven days" grew out of a misinterpretation of a painting by William Hogarth.