  The famous recurrent nova (RN) T Coronae Borealis (T CrB) has had observed
eruptions peaking at a visual magnitude of 2.0 in the years 1866 and 1946,
while a third eruption is now expected for the year 2024.4+-0.3. Each RN has
very similar light curves of eruptions that come with a fairly even-spacing in
time, for which T CrB has a recurrence timescale near 80 years. So it is
reasonable to look backwards in time for prior eruptions, around 1786, and so
on back. I have investigated two long-lost suggestions that T CrB was seen in
eruption in the years 1217 and 1787. (1) In a catalog published in 1789, the
Reverend Francis Wollaston reports an astrometric position for a star that is
exactly on top of T CrB. From his letters, these observations were made on at
least four occassions with both a large and small telescope, within a few days
before 1787 December 28. Wollaston's limiting magnitude for his astrometry is
near 7.8 mag, so T CrB would have to have been in eruption. With other
transients strongly rejected, the only way that Wollaston could get the
coordinates was to have measured the coordinates of T CrB itself during an
eruption. (2) The 1217 event has an eyewitness report written by Abbott
Burchard of Upsberg as a fast-rising stellar point-source ("stella") in Corona
Borealis that "shone with great light", lasted for "many days", and was
ascribed as being a "wonderful sign". This event cannot be a report of a comet,
because Burchard used the term for a star ("stella") and not for a comet, and
because Burchard had the omen being very positive, with such being impossible
for comets that are universally the worst of omens. The reported event is just
as expected for a prior eruption of T CrB, and all other possibilities are
strongly rejected, so the case for the 1217 eruption of T CrB is strong.
