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A PHYSICIST WRITES . . .

(April 2015)

Last month Mrs S and I experienced a couple of natural events, as you might call them, on roads in North Hants (though they neednít have happened to us there, particularly). On the first occasion I was driving from Hartley Wintney towards Reading on the B3011, just after dark. I can see now from the map that the road soon passes through Hazeley Heath, which is partly woodland.

In the headlights I detected a couple of animals crossing, some way ahead, and so I braked gently. Then suddenly they were all around us, perhaps a dozen of them, streaking across the road as fast as we were rolling along it, or so it seemed. As you will have guessed, they were deer Ė and the large variety. I have no idea how we missed them all (or vice versa). You could say that if I had braked harder, this would inevitably have put us on a collision course with one or more.

Certainly I didnít remember spotting a red-triangle sign warning of deer, either then or on previous journeys that way. But I wanted to check, so back home I started to track the road in Google Street View... and there was the sign, barely out of Hartley Wintney. Moral: even if you think you notice every sign you pass, notice harder! I can only suppose that as I had never (I think) seen deer on or near any road before, my brain had given up registering the warning. But then, what could I have done in these circumstances even if I had taken it in?

(I wonder if I risk becoming similarly blind to horse-and-rider red triangles, because when I encounter horses on the road, itís rarely near a sign. Probably the reason for this is that they tend to be placed at exits from stables and bridle-paths, logically enough I suppose Ė whereas youíre much more likely to see a horse somewhere else on its outing.)

The second natural event was a distinct anticlimax for us: the eclipse of the sun on 20 March reached its maximum while we were driving south, but below a layer of cloud, alas. If there had been a clear sky, from this part of the country we would have observed barely 15% of the sunís area left uncovered by the moon, and the drop in general light level would have been striking. But the normal brightness under cloud can vary widely, and so it seemed like just a dull morning!

Not that you should try to Ďobserveí the sun, during an eclipse, by looking at it directly. You might think that the reduced amount of light would make this safe, but it actually increases the risk of eye damage, because your pupils (and eyes) will be wider open, while the brightness of the uncovered bit of the sun will be as high as ever. It surprises me that I donít hear more of people who have injured their eyes in this way, after an eclipse.

The easy and hazard-free method for viewing such a spectacle is to fix up a pair of binoculars (or else just hold them as steadily as you can), pointing at the sun and projecting its image on to a white surface or screen. One front lens should be covered, preferably, otherwise you will get a double overlapping image. And of course you must not look through the binoculars yourself.

The further you can position them from the screen, the bigger will be the image. Ideally you want the binoculars slightly out of line with the sun Ė shifting the image sideways and allowing you to move the screen into a nearby shadow (which by the way will be deeper, and so give you a brighter-looking image, if you are able to be indoors with the sunlight coming through a window) Finally, adjust the focus to achieve the sharpest picture.

Why am I telling you all this now, when the next significant solar eclipse in the UK doesnít occur until 2026? Well, I was going to suggest first that you look out for a transit of Venus, in which the planet appears as a black dot slowly crossing the face of the sun: I vividly remember using my binoculars for this in 2004. But Iíve just discovered that the next one visible here isnít until the year 2247, sorry!

What about Mercury, then? Because its orbit is closer to the sun, normally it is a much more elusive planet in the sky: I have only ever seen it twice, in morning and evening twilight (once each). However, transits of Mercury across the sun are a different matter: I donít know why Iíve never thought of looking into or at them before, but it turns out that they are fairly frequent. The next one is in May 2016 Ė so Iíll remind you in April, in case youíre interested.

But also, binoculars may be set up, as above, at any time (when the sun is out) to observe sunspots. These vary in size and number from year to year, but when visible you can see them change position from day to day, indicating the sunís speed of rotation (which is once in about 27 days). Again I must say: donít look through the binoculars! And as a precaution against overheating them inside, cover the front lens for a while perhaps every minute or so.

Letís get back to motoring: Iím still puzzling over something that I reported here last July, namely that switching on cruise control can significantly reduce your level of concentration on all aspects of driving, as well as (or because of?) making you feel more tired. This had been demonstrated in France, in experiments on 90 people in a driving simulator. The first puzzle is that I canít uncover any previous such investigations, yet you would think that the effects of cruise control on driving performance would have been tested and monitored fairly extensively, over its long lifetime.

(Iíve read that cruise control in its modern form was devised in 1948 by an inventor and engineer, in frustration at being driven in a car by his lawyer, who kept speeding up and slowing down as he talked.)

A second question is this: if regulating my own speed is better than letting cruise control to do it for me -- presumably because I then stay more focused on whatís happening around me Ė what about the other self-controlling systems in my car, such as auto-wipers, auto-lights and even the auto-gears? Should I stop using these too? Are they all inducing me to relax and take my attention off the road?

I suppose I could try to assess their effects on me somehow. But Iím not going to test cruise control on myself, after what Iíve read and reported! Perhaps readers who do use it would like to comment...

Peter Soul

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