During my holiday in Greece, we stopped at a roadrestaurant near the town of Kalavryta. 

We were sitting on the terras, and there were bags of water hanging from the terras . The water was in transparant plastic bags. (see this picture: http://lh3.ggpht.com/_jkIfO7IHGAg/Srycwj48oaI/AAAAAAAAObo/qh60tNJ7m-g/s800/GRE_Kalavryta_2009_Sept_32.jpg )

)

We tried to come up with all kind of theories what the purpose of these bags was. 

Obviously not a first aid for a forrest fire. A thermometer to see when the first frost hits the valley,... 

At the end, we asked the owner, and he told us it was used to keep away the flies. 

I have to admit that there were no flies. But there were no bears either, so it might work for that too. 

The owner looked quite serious, so I don't think he was pulling my legg. 

So my question is, if there would be a theory why this might work, if it works at all as a fly-protection mechanism.

Does it have something to do with the defraction of the light in the water bags and the way a fly 'sees' this. 

Kind regards

Pascal

I recently saw a video on the internet of some dolphins playing with bubble rings in their water tank. These rings seemed to be just shaped bubbles but how do they form? and what sustains their peculier shape?

Here is a link to an example of the bubbles:

http://www.boreme.com/boreme/funny-2009/dolphin-bubble-behaviour-p1.php

I know that when the swimming pool is built, it is measured, and everybody is sure 50m swimming pool has 50m. But when the competisions are there, the touch pads are put on each side of the swimming pool and it is shorter! Am I right?

On looking at windows and car windscreens when it rains, I have noticed that raindrops tend to follow the previous paths of other drips when falling down the glass surface. Why is this?

During the last 100 years, humans have been burning oil, natural gas, peat and coal. In the next 50 years we will burn even more. Burning hydrocarbons produces carbon dioxide and water. How much has this water added to sea-level rise?

Alfred Jacobsen, The Netherlands

I spent time in the Scottish hills last winter and on a couple of occasions I had cause to clean my glasses in a stream that originated from melting snow, effectively at 0 °C. The water cooled the glass and its metal frame to such an extent that both lenses fell out.

But how could this happen when, if I remember my A-level physics correctly, metal should contract more than optical glass because of a higher coefficient of expansion?

Obviously this has never happened when I've been walking around under normal conditions.

Andy Douse, Drumnadrochit, Invernesshire, UK

We received some very entertaining answers to this question, but we haven't really nailed it yet. Several people called for more experimentation or wanted to know the coefficients of expansion for optical plastics so that they could be compared with those for metals - Ed

Some friends and I were drinking from a jug of water that contained wedges of both lime and lemon. All the lemon wedges were floating, but all the lime wedges had sunk to the bottom of the jug.

There were enough pieces of both for us to infer this was not just coincidence, and all of us were pretty certain that we'd seen lime slices floating before. Can anyone offer an explanation?

Bladon Mooney, Leicester, UK

Thanks to the anonymous correspondent who sent a link to a page on the Steve Spangler Science site, where the answer is tested - Ed

(Image: tellgraf, stock.xchng)

James Scowen, London, UK