Curved space-time

This trellis at The Newt near Glastonbury reminded me of the diagrams of space-time when it is curved by gravity in General Relativity!

Sun dial for the dead

Spotted in the cathedral at St Davids. It must work on light through a window. I don't think I've ever seen an indoor sundial before and certainly not one on a tomb!

Levelling the Land

Every bridge on the Lancaster Canal seemed to have a benchmark. Then the penny dropped. Benchmarks were used for linear surveys - ideal for a canal. The canal needed to be level to retain the water so surveying must have gone from bridge to bridge. But does that imply that the bridges were built as each section was dug? I suppose I'd assumed they dug the whole canal and then added the bridges but actually that wouldn't make sense in terms of access for local residents ...

Saltburn Cliff Railway

We enjoyed the cliff railway. It doesn't give the mass of an empty car but the 1500 litres of water in a full tank at the top would have a mass of 1500 kg and a weight of 14.7 kN. This must be enough to lift 12 people and overcome frictional losses. Let's estimate 12 adults at 80 kg each. That's roughly 1 tonne so say 10 kN. The frictional losses are therefore worth about 5 kN. 207 feet is around 60 metres so work done against friction might be in the region of 5 kN x 60 = 300 kJ. That doesn't actually sound that much

Polarised colours

Back to a phenomenon I've recorded before but not been able to find any theory about. Compare the bottom fence posts in the two pictures. The fence posts should be green but appear purple in the top photo. The top photo is taken through my polarising sun shades. Rotated through 90 degrees for the bottom picture. I've noticed before that my polarising filters seem to preferentially let through the blue end of the spectrum.

Robert Recorde

It was wonderful to come across this in Tenby Parish Church - the person who invented the equals sign. I suppose I have thought these things have always been there and wouldn't have a specific inventer.

Changed Meaning

The new Tullie House sign reminded me of the unit for magnetic flux density. That is T for Tesla named after the great Nikolai Tesla. I wonder now if students will think it is named after the cars.