The Gregorian Calendar was not fully adopted in Great Britain until 1752, although it had been practically universal on the Continent for over a century. With careful writers the letters O.S. and N.S. are always used and prevent any possible ambiguity. They are not used in the present work as the position of the Sun is sufficient to show which style is used. This is sometimes due to the habit of the older astrologers of registering time according to astronomical instead of according to civil usage.
Astronomical time counts from noon to noon, civil from midnight to midnight.
Consequently 6 a.m. of January 1st according to the ordinary or civil reckoning, would be 18 p.m. of December 31st according to astronomical reckoning. In this way some discrepancies can be accounted for. This again is a reversion to the Julian Calendar. From the early Middle Ages until the adoption of the Gregorian calendar in 1582, the new year began on March 25. Hence dates up to March 25 were considered part of the previous year.