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. 

Pressure and temperature

It was a mistake to store a bottle of Prosecco in the loft. The high temperatures in August must have increased the pressure of the gas in the bottle to such an extent that it was able to overcome the strength of the glass. The bottle was at the orange arrow but one shard ended up a couple of metres away by the pink arrow. The temperature must have been sustained for some time to allow the thermal energy to conduct through the glass. 

Watching the Wind on Loch Keose

The wind gusts were stirring up dark patches on the loch. These must be tilting the water in a direction that reflects less light in my direction. Then these sections moved as coherent wholes down the loch. They can't have been moving as fast as the wind itself.

Branching time lines

These apple trees at The Newt reminded me of branching lines that form in the time dimension as a result of decision making. Schrodinger's Cat is a famous example. Opening the box can be said to start two lines - or some would say two parallel universes. One would have the cat alive and the other dead. This branching is one way to get round the Grandparent Paradox and allow time travel.

Roman pottery

We had a brilliant pottery demonstration at The Newt. The potter explained that the minerals in clay can become aligned under pressure to form cleavage planes - this is what happens when slate is formed. This wouldn't be good in pottery so the point of working the clay on the wheel is to make sure the crystals don't form cleavage planes. 

Magnets

We had fun with this train set. We were trying to see how far apart the magnets needed to be before the V and the A attracted each other. It was about 1cm.

Amazingly, when the A was pulled to the V, it fired the locomotive away from the front. It turns out that the loco and the front car have same magnetic poles and are weakly repelling. I'm not sure how they can actually hold together but the impact of a push from the back fires the loco from the front.

Water jets

This feature at The Newt has jets of water being fired from the toads when sensors are triggered.

The sensors are located in recesses and seemed to be sensitive to light, or rather, the lack of it. If it were an LDR, dark would mean high resistance so could change a logic gate. The jet sprayed as soon as the sensor was covered. It wasn't triggered on the release back into light. It occurred to me that there would be a problem with this at night so either there is an overall timer or I am wrong and it is about beam breaking.

Changing wavelengths

When I was young this pylon at Barrow AFC used to house the flood lights. Now it houses mobile phone aerials. It still houses electromagnetic waves but the wavelength has increased from visible to radio wave.

Fish out of water

This amazing set-up at The Newt got me thinking. How did they get the water into the rectangular tank and to stay there? If I were doing it on a smaller scale in the lab, I'd have the rectangular tank inverted, fill it to overflowing with water, seal it, flip it over and into the water, then remove the seal.

Interesting solar panel array

This solar powered pump at RSPB Ham Wall has 3 solar panels. One faces south, one south east and one south west to ensure that one of them might be at almost full power at any point on a sunny day. Three facing south would give a higher max power output but I'd guess the average might be higher with this set up. 

Gridserve battery symbol

I hadn't noticed that the branding at the motorway services contains the circuit symbol for a cell. That's because I normally put the longer positive line on the left. I realised when I approached from the other direction.

Spiral galaxy

This foam in a stream reminded me of a spiral galaxy. One problem has been traying to explain why the spiral arms remain stable. In theory they should end up tightly wound round the centre. Apparently it might have a lot to do with density waves but I'll need to read more about that.

Iridescent tiles at Blackwell

I liked the early iridescent tiles at Blackwell. It was hard to capture the colour shifts on camera. The principle is that light reflects from the top surface and also from a layer just underneath. The light that goes to the layer underneath will have travelled a tiny bit further and so will be slightly out of phase with the reflection from the top layer. Because light is made of many wavelengths, which are the colours that we see, at different angles the path difference for one colour may become a whole wavelength so there is constructive interference and a colour is seen.

India survey

I was interested in this display at Rheged. Firstly that the survey of India was done as a series of triangles extended into long lines. Secondly, I had not come across Plane Table surveying. It seems to be a way of plotting a map at the same time as the survey measurements are taken. The table needs to be levelled and it has a plumb bob to help with this. Sight lines to points are measured. If the distance is known, the map can be made radially from a central point. In mountainous areas where horizontal distances are hard to measure you line up the same features seen from 2 known points and where the sight lines intersect, you can plot intermediate points.

                            

Heavy snow

I didn't have a tape measure with me in the Glencoe Visitor Centre but from measuring bags of sugar at home I estimate the box to be 35cm on each side. That would give a volume of 43 x 10^3 cubic centimetres and a density of snow of 28 x 10^3/43 x 10^3 = 0.65 grams per cubic centimetre. This would make it firn, which seems unlikely. But if the box is actually 40cm on each side, density comes down to 0.44 g/cm^3 which is almost down to the density of wind-packed snow. I should have taken the tape measure!

Natural ripple tank

It was amazing the way that the sunlight projected the wave pattern onto the pebbles in the ford in Glen Gartain. End of a wonderful day on Buachaille Etive Mor.

Yet another contrail

Clear skies have made it a good time for contrails. With this one it was the way it spreads apart in places and comes together in other places to make quite a regular pattern that looks like the loops I used to draw in class for stationary waves. I've always thought the contrails are manipulated by high altitude winds but I can't see how winds can pull two trails in opposite directions or push them together. 

Equinox sunset time

We revisited the 3 amazing stone circles above Boot for the Equinox. I noticed going home that the Sun still had a while to set and it was beyond 6pm. Now on Equinox, logic would say to me that sunrise should be 6am and sunset 6pm. That got me thinking. It probably works at sea level on the Greenwich Meridian in this country. Sunset is always later here on the west coast than in London. Today we are 15 minutes later than in London but that doesn't account for all of the time difference I noticed. This article explains about which part of the Sun the measurement is taken from and also about equilux day. 

Strange contrails

I was intrigued when one plane came over leaving a contrail which looked like the white line dashes down the middle of a UK road. Camera wouldn't focus and it began to break up. But then another came past very soon afterwards and did exactly the same thing - it's the one on the left in the picture. I can only imagine that there are bands of slightly different humidity up there. It was a windy day, the sort when stationary waves form in the air over the mountains. The usual sign is lenticular cloud. Maybe it was such a day but with air humidity too low for cloud formation. Then the aeroplane exhausts might seed condensation in the more humid parts.

Shap meteorological station

We know that Shap is used by the Met Office in forecasts but we've now found what must be their data gathering station in Wet Sleddale. I don't think this site is for this Met Office weather station. When I looked at it recently it said the page was last updated in May 2022. But it does say about the data package it was using which was interesting.