Approaching 100 Posts - Yes I Know, This One's Adding To It, But With Asks And Reblogs Possible On Tumblr,

"Take the aircraft engine out!" - the AP1-88 hovercraft

The Tim Traveller has just dropped a video about the massive SR.N4 car-carrying cross-channel hovercraft (which got a mention here) on display at Portsmouth, and he notes that there is still an active hovercraft service between Portsmouth and the Isle of Wight. That reminded me that I had a couple of pictures of that, and I thought I was primed for part 3 of "stick an aircraft engine in it". Two problems though.

First problem, the pictures aren't great. Taken in 2012 from the Mont Saint Michel ferry exiting Portsmouth harbour with my previous camera, which had a less powerful zoom and a lower resolution than my current one. It's still enough, in conjunction with the Wikipedia page on Hovertravel, the company that operates these vehicles, to narrow it down. The hovercraft can only be one of two vessels, the Freedom 90 or the Island Express (squinting at the bow it might be former), but the exact identity matters little. Both are of the same type: an AP1-88 built by the British Hovercraft Corporation, successor to Saunders-Roe who built the big cross-channel model.

And that's where the second problem arises: the AP1-88 is not powered by aircraft engines! It is powered by 4 Diesel engines, making it much quieter and more economical to run, while still capable of reaching 50 knots. It shows that passenger hovercraft transport is possible without gas turbines, and Hovertravel's current fleet consists of two Diesel hovercraft built in 2016 by Griffon.

Nonetheless, chalk up the hovercraft as something I have seen in action!

The best timepiece in the world (IMO): Strasbourg Cathedral's Astronomical Clock

I could go on about this thing for ages. There's so much history, so many symbols to spot, and so much information on display... This is going to be a long one.

I guess I'll start with the artistic aspect on which I have the least to say because it's the least up my alley. There's loads of mythology and Christian symbolism going on on this 18-metre tall monument, and these are the main draw for the general public, because they move around.

Like cuckoo clocks in neighbouring Schwarzwald, this astronomical clock has automatons. Every quarter hour, the lower level of the photo above sees a change of "age": a child, a young man, an adult and an old man take turns to be in the presence of Death, whose bells toll on the hour. At high noon, the upper level also moves, with the 12 disciples passing before Christ, and the rooster at the very top crows.

Moving on to what really makes me tick: the amount of information on this clock is incredible. The time, obviously, but actually two times are on display on the clock at the bottom of the picture above: solar time and official time. Given Strasbourg's position in the time zone, there is a 30-minute discrepancy between the two. Then there's all the astronomical stuff, like the phase of the Moon (just visible at the top), the position of the planets relative to the Sun (middle of the picture), a celestial globe at the base (pictures below, on the right)...

The main feature behind the celestial globe is another clock displaying solar time, with the position of the Sun and Moon (with phases) relative to the Earth, sunrise and sunset times, surrounded by a yearly calendar dial. These have remarkable features, such as the Moon hand that extends and retracts, making eclipses noticeable, and the calendar has a small dial that automatically turns to place the date of Easter at the start of each year. This sounds easy, but look up the definition of Easter and note that this clock is mechanical, no electronic calculating power involved! Either side of the base, the "Ecclesiastic Computer" and the "Solar and Lunar Equations" modules work the gears behind these features.

The accuracy of this clock and its ambition for durability are truly remarkable. Relative to modern atomic time, it would only need adjusting by 1 second every 160 years, and it correctly manages leap years (which is not as simple as "every 4 years"). It just needs winding up once a week.

Finally, the history. The monumental clock was built in the 16th century, and used the calendar dial above, now an exhibit in Strasbourg's city history museum. It slowly degraded until the mid-19th century, when Jean-Baptiste Schwilgué restored the base and upgraded the mechanisms. The "dartboard" on the old dial contained information like the date of Easter, whether it is a leap year, which day of the week the 1st January is... - all of which had to be calculated by hand before the dial was installed! - and was replaced by the Ecclesiastic Computer, which freed up the centre space for the big 24-hour clock, complete with Solar and Lunar Equations.

As you may have gathered, I am a massive fan of this clock. Of course, nowadays, all the imagery and information would easily fit into a smart watch, but a smart watch isn't 18 metres tall and powered by gravity and gears!

Everything is ready for Tuesday! How this particular configuration works, as well as the one below, will be covered - we can talk about it on here too afterwards if anyone's interested.

C'est avec grand plaisir que je présenterai le mardi 16 avril à la Maison Universitaire France-Japon de Strasbourg une conférence sur la géométrie pendant la période d'Edo, avec en support le sangaku de Kashihara. Entre grande Histoire et petits calculs. Lien vers les détails 4月16日(火)、ストラスブール市の日仏大学会館に江戸時代の算額についてコンファレンスをします。楽しみにしています！ Looking forward to giving a conference on Edo-period geometry on 16 April at Strasbourg's French-Japanese Institute. Expect a few posts about Kashihara around then. Has it really been 6 years?...

Sangaku Saturday #8

Having established that sangaku were, in part, a form of advertisement for the local mathematicians, we can look at the target demographic. Who were the mathematicians of the Edo period? What did they work on and how?

The obvious answer is that the people in the Edo period who used mathematics were the ones who needed mathematics. As far back as the time when the capital was in Kashihara, in the early 8th century, evidence of mathematical references has been uncovered (link to a Mainichi Shinbun article, with thanks to @todayintokyo for the hat tip). All kinds of government jobs - accounting, such as determining taxes, customs, or engineering... - needed some form of mathematics. Examples above: 8th-century luggage labels and coins at the Heijô-kyô Museum in Nara, and an Edo-period ruler used for surveying shown at Matsue's local history museum.

As such, reference books for practical mathematics have existed for a long time, and continued to be published to pass on knowledge to the next generation. But sangaku are different: they are problems, not handbooks.

More on that soon. Below the cut is the solution to our latest puzzle.

Recall that SON is a right triangle with SO = 1 and ON = b. These are set values, and our unknowns are the radii p, q and r of the circles with centres A, B and C. While these are unknown, we assume that this configuration is possible to get equations, which we can then solve.

1: The two circles with centres B and C are tangent to a same line, so we can just re-use the very first result from this series, so

2: Also recalling what we said in that first problem about tangent circles, we know that

Moreover, PA = AO - OP = AO - CQ = (p+2*q) - r. Thus, using Pythagoras's theorem in the right triangle APC, we get a new expression for PC:

since 2(p+q)=1 (the first relation). Equating the two expressions we now have of PC², we solve the equation for r:

again using the first relation to write 2q-1 = -2p.

It only remains to find a third equation for p to solve the problem.

Feeling rather non-committal today, so here are some flowers from the Expo '70 Commemoration Park near Osaka. This is probably going to start a mini-series because the place is huge, so more information will come later.

French and German cross-border railcars

Just on the French side of the border, Wissembourg station sees French TERs arriving from Haguenau and Strasbourg, meeting German Regionalbahn from Landau and Neustadt. When a French service doesn't cross the border itself, SNCF and DB services are often synced up, giving us the chance to see both companies' cross-border efforts side by side.

The B 85500 is a brand-new bi-mode (electric and Diesel) multiple unit from the Alstom Régiolis family. While not the first international Régiolis - a tri-voltage electric version runs between Évian and Geneva -, the B 85500 adds autonomous Diesel power. With 30 units on order, it aims to revive and/or intensify cross-border routes into Germany. I was under the impression there was a bit of a gathering at the front end of the train, maybe local politicians marking the type's first visit to Wissembourg?

On the German side meanwhile, we have a standard railcar for what DB regard as a relatively low-density non-electrified regional route, which was closed to passengers for over 20 years between 1975 and 1997. The BR 628/928 (628: power car, 928: trailer car) is a 1980s design. Besides the lack of low floor, there's not a lot wrong with them, and they have comfortable, current DB Regio interiors. More recent types have been used, and if a plan to electrify Landau and Winden stations to allow charging of battery-EMUs goes ahead, there could soon be the latest trains on the German side of Wissembourg station too.

Which brings us to our "I beg your pardon" of the week:

Le moulin rouge du Moulin Rouge a perdu ses pales!

Was going to take a break from posting today, but we had a bit of breaking news out of Paris: the famous cabaret Moulin Rouge's red windmill has lost its sails! They fell off at around 2 in the morning apparently, cause unknown. No injuries.

Article France Bleu Paris

Japan's first Concorso d'Eleganza

A Concorso d'Eleganza is basically a beauty pageant for historic cars. Based on similar contests for horse-drawn carriages, called Concours d'Élégance, the Italian name references the fact that the most famous competition in the genre for cars has taken place in Italy since 1929.

The Japanese version was launched in 2016, with the amusingly-named "Artistic Cars at the World Heritage, since 2016" exhibit at Nijô-jô, Kyôto. I say amusing, because they were using the "since 2016" tag in 2016, and... it hasn't used that name since! Nonetheless, the sight of these immaculately preserved cars in the lovely palace gardens was impressive.

Among the cars built between the 1950s and 1990s, there was an exhibit with rare Zagato specials. Particularly obscure is the Autech Zagato Stelvio, shown above and below. Of the three names, Zagato is the best known: they are an Italian coachbuilder, who make unique bodywork. Autech is a Japanese tuner, working most closely with Nissan. And the Stelvio is a late-80s mix of all that: a modified Nissan Leopard with very unique design choices, such as the wing mirrors in the fenders.

The Concorso d'Eleganza Kyoto is set to resume this year, having been put off due to the pandemic and the restrictions surrounding it since 2020. The principle hasn't changed: they're going to show some remarkable historic cars in a historic Japanese setting - at Nara this time.

Statement on my Instagram regarding Meta's moderation policy updates

Meta's updated policy on hate speech can best be described as... "weird", I guess.

The highlighted sentence, which is factually inept, is what is causing the uproar. Political and religious discourse on homosexuality, or any other group of people for that matter, does not use, and has never used, unsubstantiated allegations of mental illness or the word "weird" in a light or "non-serious" way. They are always used with the ulterior motive to discredit and stigmatise, and make exclusion of said group, a core element of the law & order doctrine they aspire to. But this is now explicitly permitted on Facebook and Instagram.

The law in most European countries currently does not allow this double standard on hate speech. While this does offer protection to all citizens in the applicable countries, the fact that Meta is in open disagreement with these protections, regardless of the reason, is something to think about.

I will be evaluating my presence on this platform [Instagram] in the coming days and weeks. Meanwhile, a normal blogging schedule will be maintained on the companion Tumblr. Cheers.

Coot chicks in Schaffhausen and herons in flight at Konstanz. That is all for today.