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.