To Sir Thomas Roe. Until 1752, when by Act of Parliament the first day of
January became the first day of the year, the year began on March 25th and
ended on the following March 24th. What to Donne was "the last (day) of
1607" would be to us March 24th, 1608. Since 1752 therefore it has been a
common practice in referring to dates falling between January 1st and
March 24th inclusive of all years previous to the year 1752 to give both
years. So we would give the date of the execution of Charles I as January
30th, 1648/49.
"The Mask" is possibly Ben Jonson's _The Hue and Cry after Cupid_,
"celebrating the happy marriage of John Lord Ramsey, Viscount Hadington,
with the Lady Elizabeth Ratcliffe," of which Rowland White wrote to the
Earl of Shrewsbury, "The great Maske intended for my L. Haddington's
marriage is now the only thing thought upon at Court."