Light detection in the eye

 

This explained clearly how we see colour. I read an interesting report in Physics World recently about seeing brand new colours. Each type of cone cell detects over a range of wavelengths. There is overlap of these ranges which means that certain wavelengths trigger two different cone cell responses. This masks them so we don't see those colours independently. Researchers have used very narrow laser light to hit single cone cells so that the response comes from only one type of cone cell, avoiding the overlap problem.

Dog Vision

 

The exhibition at Tullie House on Colour was a lovely mix of basic science and art. I was left playing spot the difference with these pictures but I did figure out which end of the spectrum is missing for dogs.

Colour Blindness

 

Doing the colour blindness test is one of my earliest memories from Primary School. Interesting to see them again all these years later.

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.

Vector Field

I loved the two large concrete arrows on Mawbray Banks, used to guide bomber training in the war.