Re: Problem with a Barometer

[brian whatcott <inet@INTELLISYS.NET>]

At 09:24 5/4/99 -0700, Roger Haar wrote:
> Hi,
>
>        I have an odd problem with a mercury barometer.  It
> reads too large of an atomospheric pressure.  Here at the U
> of AZ the Atmospheric Science Dept has two nearby stations
> from which I can get readings.  These report something like
> 27.2 inches   ( NOT corrected to sea level) and I get 29.5
> inches.
>
>        I checked the scale using a meterstick and two agree
> to within a millimeter which is the error in my reading of
> the meterstick.  I have checked for bubbles or breaks in the
> mercury column but there are none visible. ....

> Roger Haar

I guess it falls to me to ask the potentially offensive
or insulting questions and make the corresponding observations:
 - I am after all an outsider here:

1) The height of interest is the distance from the lower to the
upper mercury surface.
 It is not enough to rely on the default surface level of a wooden,
leather or glass reservoir, no matter how wide its surface area.

2) the stick must be strictly vertical. A plumb bob will verify this.

3)If these two criteria are met, then we can say confidently
that either the mercury column is 'sticky' with impurities,
or it has alloyed with a less dense material.


brian whatcott <inet@intellisys.net>
Altus OK