Bressay: burnt mound update

I posted about burnt mounds after our first trip to Shetland. This time, we found an amazingly complete excavated and rescued burnt mound by the ferry on Bressay.

Rocks were heated in the furthest chamber.

The hot rocks were transported forwards and put into this water tank at the front. The tank looks to be 1m wide by 2m long by 30cm deep. That makes 0.6 cubic metres or 600kg of water. I was talking about heating 5kg. This is over a 100x smaller. So we would be talking about maybe 300kg of rock, or 100 large pebbles, to get the heating to 60 oC.

Looking for Hawaiite on Canna

 The exposed bedrock on the top of Compass Hill was very friable. This sample dislodged under me!

The BGS viewer tells me it is Hawaiite but that it is aphyritic. I had to look that up. It means that it doesn't have phenocrysts - crystals that are obviously much larger than the other grains. I can see some much larger bits in this rock. It probably means that they don't count as phenocrysts. See here for Hawaiite from Rum. Here for details of what Hawaiite is.

Scattering: Fair Isle at sunset

It was amazing to line up the sunset with Fair Isle from the ferry. In fact, the sun set 3 times: it disappeared then the relative movement of boat and sun lined up the very top of the sun with a lower gap on the island so it could disappear again!

Focusing on the droplets on the outside of the window gave a lovely example of scattering. Light from the sun hits the droplets and then is re-emitted to my eye. This is like what happens with the atoms in the high atmosphere. Rays of light from the sun that are not coming in my direction are absorbed and then re-emitted back in my direction.

Light sensor on water bottle filler

I was having trouble with the bottle refiller in the ferry terminal in Lerwick. Then I noticed the black dot at the bottom of the blue bottle graphic. Turns out it must be a light sensor which activates the water flow when it is dark enough. My bottle was completely clear so it wasn't blocking the light. Putting my hand around the bottle rectified the problem. I wonder what happens at night?

Data centre power use

I saw this article a few weeks back about data centres using up 18% of Ireland's electricity. I have been after figures about this sort of thing for a while and have now discovered this brilliant book by Mike Berners-Lee. He calculates that data centres use 1% of the world's electricity with countries that host many centres for tax reasons having a far higher percentage of their electricity used.

Wind power on a narrow boat

I saw this boat in Oxford. I was wondering what the power rating of a turbine like this would be. I found this site. It sounds like 130W. They do have data to back up what they are saying. I am wondering whether they mean Amp-hours Ah rather than Amps per hour because battery storage is measured that way. I found this to look at 

https://www.drivingelectric.com/your-questions-answered/325/what-are-kwh-and-ah

Robert Hooke

I haven't really ever taken much notice of Robert Hooke. Hooke's Law always seemed trivial and obvious. Newton's work is seen as so vast and foundational. I hadn't realised that Hooke had studied at Oxford. With Newton at Cambridge, there's another potential cause for rivalry. He does seem to have been involved in a lot of fields.