All along the watchtower

The hidden castle 

 This past Sunday we found Leiden Castle.  It dates from the 13th century and it's basically just an open roofed cylinder on top of a man-made hill.   At the confluence of the Oude Rijn and the Nieuwe Rijn.  

The thing is completely hidden from the street.  The ``modern'' buildings around it, many also hundreds of years old,  completely hide it.  So you come up on it through a little back alley.  It's really quite charming.  

Cultural observation

The Dutch are wonderfully weird

In the middle of the castle sits this sort of benchlike sculpture.  I had to get within a few meters before I realized that it's a wooden tube of toothpaste.  The paste coming out the end is marble.   They put a sculpture of a half used tube of toothpaste in the middle of an 800-year-old castle.  Cause, y'know, it's cool.  You know the drug laws here are very liberal.  And it gets better...

A few meters away is more marble:

Yep, that's right. Very liberal drug laws.  Whatever hard edges the Dutch national personality may have, stuff like this more than makes up for it.  Did I mention the camel in Amsterdam I saw in January? 

A positive derivative

My second lecture in my short series on inverse problems was better attended than the first.  We're up from eight to ten.  It seems to be going ok.  I got through a review of the construction of pseudoinverses and then blasted a little too fast through inversion the Radon transform again. 

Word of the day:

roodverschuiving: red-shift.  Het model Hubbel verbindt roodverschuiving met galactische afstanden. The Hubbel model connects redshift and galactic distances.