>
> Peter,
>
> You are discribing a hygrometer or wet and dry bulb thermometer.
> You also need a chart which tells you the relative humidity corresponding
> to the difference between the wet and dry bulb reading. This instrument
> is not as accurate as a sling psychrometer which also uses a wet and
> dry bulb, but is rigged so that the thermometers are rotated very
> rapidly around an axis by means of a handle (originally they were "slung"
> around on the end of a cord or rope).
>
> Bob Schramm
Yes, we slung ours round in the lab on a bit of string. My old copy of WHJ
Childs Physical Constants that I got at school (6th ed, revised, 1951) has a
little table with 'dry bulb temp' across the top and 'depression of wet bulb'
down the side. Just find the appropriate row and column and read where these
coincide. So here the current temp is about 15 degrees Celsius, a wet bulb
temperature of 8 degrees (7 degrees depression) corresponds to a relative
humidity of 36.
I think when we did it at work we had a larger - and thus more accurate table
- the one here only lists room temperatures every 5 degrees from 0 to 40.
What could be easier? Most of us already own a thermometer, piece of string,
rubber band and small bit of damp cloth, so the cost is zero. That's the kind
of equipment I like.
Peter Marshall
On Fixing Shadows, Dragonfire and elsewhere:
http://faraday.clas.virginia.edu/~ds8s/
Family Pictures & Gay Pride: http://www.dragonfire.net/~gallery/
and: http://www.speltlib.demon.co.uk/
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