On Thursday we took a 4-hour train ride back from Edinburgh to London; on Saturday I took a plane back from London to Montreal, and today I’ll take a train from Montreal to Kingston. So I spent a day and two partial days in London as the last couple of vacation days. There is a lot to see in London, plenty for a month (or a year!), so we had to pick just a couple of highlights

On Thursday it was around 4:30 or 5 when we got settled in our hotel near the Bayswater tube stop in Kensington, so we took a walk around the Kensington Gardens park. We saw the outside of Kensington Palace; it’s open to the public but was closing by the time we got there. The sun was low over the building at the time, so I don’t have a good photograph.

Of the many things we could have done on Friday, I had to pick two, and the one I most wanted was to see Babbage’s Difference Engine , one of the oldest computing machines (the oldest analog one being the Antikythera device ), and straddle the Prime Meridian in Greenwich. The piece of the real difference engine is housed in the Science Museum’s Making the Modern World exhibit, but there is also a complete model built in 1991, located on the second floor standing alone at the top of the stairs. The conclusion of the 1991 project was that building the Difference Engine was well within the capabilities of Victorian engineering, and the project’s failure had much more to do with financing, politics, and Babbage’s difficult personality. If it had succeeded, and managed to compute and print the kinds of enormously valuable tables it was meant for, it’s conceivable that the British Government might have been willing to fund the Analytical Engine , which would have been the first programmable digital computer, and the world would be a very different place.

Next to Difference Engine #2 (the modern implementation) was the clockwork museum, formerly housed in the much less prominent building of the very old clockworker’s guild. I learned more about the creation in Britain of the first maritime clocks, which let navigators compute longitude quickly and accurately by comparing local time with a fixed reference point — the Prime Meridian in Greenwich. That was my second-highest priority for Thursday.

Greenwich is about 40 minutes by Underground and Docklands Light Rail from South Kensington (which has several museums) so there-and-back took a noticeable bite out of our day. Nevertheless I got my I-was-here photo:

Of course the Prime Meridian runs halfway around the world, and I could have picked a spot outside the museum area that I could have verified with the GPS on my phone, but then I would have missed the tour of the Royal Observatory and not have had photo of the official marker in the ground.

The observatory includes one of these:

It’s a ball that drops at a specific time each so ships on the Thames could set their chronometers, in the days before electronic clocks synchronized via lightspeed signals and atomic clocks. In Edinburgh there’s another of these, accompanied by the firing of the 1pm gun (said to have been picked as the time of day so the frugal Scots could pay for only one firing instead of twelve).

The museum also includes more details on the creation of the first maritime chronometers, and their evolution after that. John Hamilton won a prize for making a series of four proof-of-concept implementations that were tested out by the Royal Navy, but a lot of other people contributed refinements that made them better and more affordable.

On the waterfront near the DLR stop is Cutty Sark, one of the last and fastest tea clippers. We only stopped long enough for a couple of photographs:

On Saturday we could only fit in one trip, so I chose Tower Bridge.

This is the I-was-here photo from having walked most of the way across the bridge; we got to the end, walked down some step and across to the other side, and walked back. In between I took a photo of the Tower of London viewed from the base of the bridge:

Near the Tower Hill Underground Station is a ruined postern gate discovered during the subway’s construction:

The trip to the airport and the flight home were uneventful, arriving at the gate about 8:30pm and clearing customs quite a while later. I stayed at the Sheraton airport hotel since there were no trains home that late, and this morning used a very comfortable desk to write this likely-last vacation blog post. It’s conceivable that I’ll have a couple of retrospective posts in a few days, but since I will be back at work tomorrow that may not happen.

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