Tanker earth wire

We were parked behind this tanker when I noticed a coil of green and yellow wire on the back. That's the Earth wire. The process of driving on insulating tyres causes charge to build up on a vehicle, giving it a high potential. Earth has a potential of 0V. This can cause sparks as the potential difference causes electric charge to flow, with maybe explosive consequences if the tanker contains powder or flammable liquid. The Earth wire must be connected to the ground before the vehicle is emptied.

Gregorian Calendar

I spotted St Gregory in the window of the church at Welford Park, of Bake Off fame. He is the patron saint of this church. In the window, he is a pope and I assumed he was one responsible for the Gregorian Calendar. I was only 1000 years out. It was a later Gregory who instituted the reform whereby the leap year day is removed on the start year of every fourth century. There was also some correction of dates to get the Spring Equinox back to March 21st. This is all important to get the date of Easter correct. If you're not familiar with that controversy, try Bede's Ecclesiastical History of the English People. It was this first Pope Gregory who sent the missionaries to the Saxons that led to the controversy in the British Isles. The calendar stuff is all because the orbit of the Earth round the Sun is not perfectly a whole number of rotations of the Earth. 

km/h

A rare km/h speed limit sign for the UK. But on a water way. 8km/h seems a random choice but the significance is that it is 5mph.

Stationary waves on the Eden at Rockcliffe

This morning the tide was coming in up the Eden backed by a strong wind. As we walked downstream, the water stopped flowing out to sea. Instead we found a patch of choppy water where the waves didn't make any progress. Stationary waves form when two sets of waves travelling in opposite directions run into each other. In the lab, these have to be of same speed and frequency. I doubt that's strictly true here. In such a stationary wave pattern, I wonder how deep it goes down and whether there is a net flow of water below. It would need to be out to sea because otherwise the water down the Eden would spill over the sides. Also whether the particles at the surface move through the pattern in equal numbers in opposite directions or whether they are stalled and vibrating up and down.

Literal geological map

Outside the Bill Bryson library in Durham there is a geological map of the British Isles set into the pavement. What is best about it is that each part is made of the rock that is found there. This is Cumbria. So there is the ring of sandstone with limestone flanks and different igneous in the middle. A great way to visualise what is going on.

Generator and diodes

I loved this dynamo setup in the museum in Kirkwall. The lights are diodes so they only allow current to flow in one direction. One has been set to allow current forward and the other to allow current back. It is a brilliant way of showing that the direction of current depends on the way the dynamo is rotated.

Barytes - Potts Gill mine

Potts Gill mine above Caldbeck produced barytes. I've known the name for decades but never studied it. Turns out it is barium sulfate. It has a whole series of applications including fillers in paint but I have come across barium meals for CT scans because it does not allow X-rays through. I've also been reading about its use in drilling fluid where its density helps to stop fluids leaking out of the rocks into the borehole and causing a blow out.