Focus

Latin pupa, and it's diminutive form, pupilla, mean a young girl, a tiny doll, a minor. If you look into someone else's eye, in the right light, you see a tiny image of yourself, a pupilla, reflected from the darkness in the centre. So the same word, pupilla, was applied to the eye's centre, the pupil

This is not reflection, of course, it's refraction - the rather mysterious bending of light that happens when it crosses a boundary between two substances, such as light and water - the phenomenon that means shooting fish in a barrel wouldn't be as easy as people make out, I think. The droplets, then, working like a lens, refracting light on the way in and out of the water, focussing the light into an image, picked up by the camera. A micro-brewery

We are living through the week or two that happens in most winters, when the sun disappears and life becomes a cold, damp continuum varying from dull to grey to dark. The wind has dropped too - very appropriate weather for the energy secretary to be questioned about his net-zero strategy. It's true that UK gets a lot of wind, and we have a lot of places to put turbines, as well as plenty of places we can put solar panels. But there are periods most years when the sun does not shine and the wind does not blow; infrequent is not the same as totally absent

The minister needs straight answers to this problem if he is to be convincing. A "strategic reserve of gas-fired power stations", to run for the ten days when we need them, will be very expensive. So is battery storage; so is nuclear. Inter-connectors across a wider range of Europe, and North Africa will help to reduce the frequency of low-renewables days, but not eliminate the risk, I think. It may be diminutive, but it is definitely there. What, exactly, are we going to do on black, still days like this, and has someone done the maths?