Re: bubbles in my compass

[Mark Sylvester <msylvester@gn.apc.org>]

> > I am sure that the plastic      of your compass face is soft enough
> > that the oil in the compass is essentially in equilibrium with ambiant
> > air pressure.  Thus, pressure as well as temperature can play a role in
> > solubility of whatever gas is involved.


Hmmm... you have me squeezing the faces of the empty capsule 
of a broken compass. The walls are really very rigid. I can 
imagine they would flex (I mean - everything does) but only with 
a significant delta P across them.

Yesterday I took out my mapping compass, which has been lying 
quietly in a desk drawer since I last used it in December. Then 
I was working on a map not far from here, about 100m higher than 
where I live. It was also cold - round about zero Celsius. I 
remember being very bothered by the big bubble which was 
upsetting the disk with the degree markings when I used it then. 
Well, the bubble, very topically, has disappeared!

Mark.

Mark Sylvester, Duino, Trieste, Italy.