"Dave Martindale" <davem@cs.ubc.ca> wrote in message
news:bhhkhb$m54$2@mughi.cs.ubc.ca...
> "Shiperton Henethe" <shiphen@yahoo.com> writes:
>
> >> One problem of helium is its ability to permeate many materials, which
may
> >> cause a problem. The single atom helium molecule is much smaller than
the
> >> twin-atom nitrogen molecule.
>
> >True though arent binoculars all metal and glass?!
> >Actually Ive no idea what the seals are made of.
>
> Normal helium-neon laser tubes enclose the working gas in glass and
> metal.  Yet the helium slowly diffuses right through the glass,
> eventually rendering the tube useless.  That's one reason the tube is an
> inch or more in diameter, though the active laser bore it tiny: the
> larger volume of gas makes it take longer for the tube to fail.

Right through glass? crikey. I stand corrected.
An likewise Hydrogen no doubt...
What about a vacuum, then - suppose the focus
mechanism would be tricky.

But thinking about it if you did start with
Helium what would happen? If helium could get
out but nothing could get back in, then a
partial vacuum would be set up, this dimishing
the flow of helium, but in either cas not
increasing the weight of the device...

A bit tenuous?

Okay I give up. Maybe Nitrogen will have to do after all.


ship