Irish eyes are smiling

We started the day with a cab ride to suburban Dublin for some mathematical history.  We took a cab ride for a few miles outside the city center where we a staying to see the spot of a famous mathematical moment.  As he was walking, Irish mathematician Hamilton discovered quaternions and, without pen and paper to record his discovery, he used the stones of the nearby bridge to record his breakthrough.  This is commemorated on the bridge with a stone plaque.  The plaque is a bit hard to read, but states:

Here as he walked by
on the 16th of October 1843
Sir William Rowan Hamilton
in a flash of genius discovered
the fundamental formula for
quaternion multiplication
i² = j² = k² = i j k = −1
& cut it on a stone of this bridge

Quaternions are numbers that extend complex numbers, having 4 parts rather than 2, as a 4-dimensional entity.  The directions for each component are indicated by the numbers 1 and the letters i, j, and k. They have applications in physics and mathematics, particularly in modeling rotations in three-dimensional space.

The commemorative plaque.

Broombridge, where the plaque is located.  This bridge crosses over a rail line and the Royal canal.  A multiple use path follows along the canal, making this a pleasant little spot.  There were swans and ducks in the canal, but were a little camera shy.

Our next destination was the National Museum of Ireland - Decorative Arts & History.  This museum contains decorative art from Ireland and is housed in an old army barracks.  There is also some historical military displays and information about Ireland's partial independence from Britain.  There was some Celtic interlace, but not like the archaeology museum we visited yesterday.  We also had a late lunch at their cafe.

We walked from there back towards the hotel and did a little shopping along the way.  This is the first day we have had where it has been cool enough to walk around without breaking a sweat.  Amy's Irish eyes were smiling!  I bought a compass for my wristwatch strap to help with orientation in the ancient cities of Europe.  The GPS on my phone works most of the time, but does not always show the correct location or direction, especially in buildings or narrow streets.  We walked by the Jameson Distillery, but opted out of the tour.  We stopped for drinks and a snack at the local Hard Rock Cafe instead.

A view of Dublin.

River Liffey.  This river runs through Dublin and its bridges are quite busy.

Our final stop was at the Chester Beatty Library.  This library, now a public collection, was acquired over the lifetime of Chester Beatty.  He had a particular interest in ancient books.  We saw some of the earliest known versions of New testament writing, dating back to about 200 AD.  There were also many illuminated texts, etchings, and paintings on display.  This we adjacent to Dublin Castle.

Part of Dublin Castle.

We came back to the hotel to rest a bit then had dinner at a local pub.  We need to leave the hotel at 5 am, so we spent some time packing and getting organized.  Amy has expanded her suitcase with lots of items we have picked up over the past 10 days.  It seems doubtful the suitcase will close.  "I think I'm going to make it." says Amy.  Tonight it closed.  We'll see after one more day in London!

I have been hearing rain falling as I finish this post.  There was also a flash and the sound of thunder.  This is the first rain of any significance since we arrived.  Hopefully we will not have to wait in the rain for our bus to the airport tomorrow morning.