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From article <1993Jan4.223650.9171@phx.mcd.mot.com>, by schuch@phx.mcd.mot.com (John Schuch):

> Excuse me but if you cool the sensor by placing it in an airstream, your
> not reading the actual temperature of the air.

At supersonic velocities, this is indeed the case, as friction
will have an effect e.g. surface heating of meteors, rockets, etc.
At less drastic temperatures, airflow will cause the temperatures
to equalize.

> Reading a sensor cooled
> by an airstream, by itself, tells you nothing. If you measure one sensor
> in an airstream and another one nearby but shielded from the air stream,
> you can determine the speed of the airstream.

Not without knowing the atmospheric pressure, the pressure right
at the sensing element, the relative humidity, and some higher math.

> Other than that, I don't
> know why you would want to cool the sensor.

I think that the original poster wanted it to merely reflect
the outside air temperature, and did not want to cool it in
any way.

> You will note that weather stations keep the thermometer in a little
> louvered box to break-up the wind. Even high-end indoor/outdoor
> thermometers include a little shell to place over the external
> sensor.

The purpose of the box is to keep the sun from shining on the element,
which would heat it up and introduce error into the measurement.
The purpose of the louvers is so that some convection can occur, thus
prohibiting the air inside the box from heating up.
-- 
Mark Walsh (walsh@optilink) -- UUCP: uunet!optilink!walsh
AOL: BigCookie -- Amateur Radio: KM6XU@WX3K -- USCF: L10861
"What, me worry?" - William M. Gaines, 1922-1992