Jean Cunningham, by email, no address supplied

I know that the dimples on golf balls allow them to fly further. But before dimples, protruding nodules were used. What is the difference between the two? Why are dimples better than nodules?

Billy Vine, Cardiff, UK

Alan Glass, London, UK

my reasoning is by comparison with kangaroos, which also have muscular legs, long tails, & little stubby arms..

During a recent lecture on the use of confocal microscopes, we were told that red light penetrates further into tissue than blue and green light.   This was demonstrated by the fact that a red laser is still visible when shone through a finger, but a green one isn’t.   This contradicts the loss of red light that is observed as you descend underwater; everything appears blue at depth when scuba diving.   Why is this?

What gives chestnut mushrooms their brown colour? The colour can be wiped away, leaving what looks like a standard white mushroom.

Barry Strong, Manchester, UK

I work as a wildlife tour guide in the Scottish Highlands so I travel widely in remote corners of the northern Highlands and islands.

On two occasions in late 2009 I have come across a pile of odd objects (see photos) scattered on the ground. The first time was on a remote island in the Orkneys; the second was a few weeks later at an altitude of around 900 metres in the Cairngorm mountains.

Had they been near a road or habitation I would probably have dismissed them as just some sort of household electronic debris, but in both cases they were miles from anywhere. The pile I found in the Cairngorms was at least a 2-hour walk from any road, track or building.

They appear to have a burnt and pitted charcoal-like solid centre encased in a hard, plastic-like cover. The ones in the Cairngorms also had some small charred battery-like cylinders with them.

Can anybody suggest what they are, and why they ended up in such unexpected locations?

John Poyner, Nethy Bridge, Highland Region, UK

Is there any evidence that piped music in shops, pubs and similar establishments increases sales? I avoid such places even if that is inconvenient or involves extra cost.

D. G. Shotton Havant, Hampshire, UK

Virtually every anti-bacterial cleaning product that I buy claims to that it will kill 99.9% of bugs. So my questions is - what type of bacteria or viruses are the 0.1% that these products can't kill? They really must be the sort of thing that you wouldn't want to meet down a dark alley.

It's a popular cliché to say that you wait ages for a bus, and then three turn up at once. But is there any truth to this? Or is it a false impression formed because we notice coincidences more than other events?

If true, are there laws governing this behaviour, and are there any natural phenomena that obeythe same principles?

Clare Redstone, London, UK