Mirror warning ..

[T i m]

Hi All,

A mate told me today that he has a 'mirror in the bathroom' ( that might make some good lyrics for a Ska band ) that can be moved around on a sort of cantilever arm system and reversed to give a magnified effect.

His mussus left the bathroom window open when the were doing the London > Brighton Cycle ride the other day and when they got home he noticed there was a burnt track across the frame (melted uPVC and black soot marks) and the rubber seal was sliced in half!

The mirror had magnified and relected the sun onto the fame and had it been painted wood might of set fire to the gaff? ;-(

Just thought I'd mention it ...

All the best ..

T i m

[Ed Sirett]

A friend of my wifes had here flat just about totalled by such a mirror. It is believed that the beam caught the curtains.

Any truth you think to the urban myths about those twee bobble glass panes doing the same?

[Ian Stirling]

No, or at least not easily. The focal length of the bubbles is some 1cm or so, and the area tends to be around a half a centimeter square. So, you get tiny, usually badly formed as the lenses are badly shaped points where the sun is brought to a focus about a centimeter from the glass.

[adder]

Aren't those mirrors convex -i.e any light shining on itis dispersed not focussed on a particular point??? i.e. opposite to a satellite dish.

[Chris J Dixon]

Chris

[Brian S Gray]

A lady round here was reputed to have lost a fur coat which she left behind such a window. With regard to the original theme, we were once lucky to get away with a singed bedspread when a mirror was placed nearby before we went out of the house. Our adjustable >

mirror reflects onto tiles and I hope that protects us.

[Ian Stirling]

Possible. Imagine trying to on purpose light a fire with a .8cm diameter lens. It's going to be hard, and you'r going to have to find some decent tinder. I suspect a fur coat may qualify.

[Ed Sirett]

No. I'm talking about the type of glass where the bobble is about 5cm diameter. I take your point that the focal length might be fairly short.

[Ian Stirling]

Hmm, I've never ever seen that.

Must have been my sheltered upbringing. A 5cm lens will have a significantly longer focal length, as the total glass thickneess cannot vary much. Say 30cm? The lenses are probably going to be badly formed, which will greatly reduce the effect, as you won't get one neat focal point from the sun, but an extended blob that isn't nearly as hot.

[The Natural Philosopher]

Yes, and more easily than I ever expected.

I had, fortunately, specified a fireproof lining in my curtains, and one fine winters day, I smelt scorching, and there was a 2" long charred stripe across one.....

No, it's all over the bloody place. They are in no way a perfect lens.

Mine was about 4-6" away - a sill width holding a piece of card there afterwards showed that part of the 'lens' - I suspect the outer part covering a greater area, and hence more dangerous - was responsible. The inner part, of a focal length as you describe, played no part.

And a larger hotter equally badly formed one up to a foot away.

[The Natural Philosopher]

huh? The centre section of bullion glass is about 6" across.

Or any flammable curtains.