the early part of the above-cited month, on my coming down to
breakfast, your (then) little brother William Edwin, and yourself,
used to ask me, 'Well papa, can you multiply triplets?' Whereto I
was always obliged to reply, with a sad shake of the head: 'No, I
can only ADD and subtract them,'

"But on the 16th day of the same month--which happened to be Monday,
and a Council day of the Royal Irish Academy--I was walking in to
attend and preside, and your mother was walking with me along the
Royal Canal, to which she had perhaps driven; and although she talked
with me now and then, yet an UNDERCURRENT of thought was going on in
my mind which gave at last a RESULT, whereof it is not too much to
say that I felt AT ONCE the importance. An ELECTRIC circuit seemed
to CLOSE; and a spark flashed forth the herald (as I FORESAW
IMMEDIATELY) of many long years to come of definitely directed
thought and work by MYSELF, if spared, and, at all events, on the
part of OTHERS if I should even be allowed to live long enough
distinctly to communicate the discovery. Nor could I resist the
impulse--unphilosophical as it may have been--to cut with a knife on
a stone of Brougham Bridge as we passed it, the fundamental formula
which contains the SOLUTION of the PROBLEM, but, of course, the
inscription has long since mouldered away. A more durable notice
remains, however, on the Council Books of the Academy for that day
(October 16, 1843), which records the fact that I then asked for and
obtained leave to read a Paper on 'Quaternions,' at the First General
Meeting of the Session; which reading took place accordingly, on
Monday, the 13th of November following."

Writing to Professor Tait, Hamilton gives further particulars of the
same event. And again in a letter to the Rev. J. W. Stubbs:--