Wbd

[AMRAAM]

General Meteorology

Hi there "Wrong way up"

This is from "General Meteorology" Page 33 Chap 6.15 (except the spelling errors)

" If the air passing over the wet bulb thermometer is not saturated, evaporation of water from the muslin takes place. As the faster moving water molecules esacpe into the air, they take heat energy with them.
The temp. of the water which remains on the muslin therefore falls. The latent heat of the vaporisation is carried away by the molecules that have been convereted to water vapour. If evapration occurs, the wet bulb temp. will therfore be lower than the dry bulb reading.
The difference between the temp. of the dry bulb and the wet bulb thermometer depends on the rate of evaporation. it is known as the wet bulb depression.wet bulb depression

And there is a bit more. The gen and Aviation met books are available at most avaition or tech book stores. I highly reccomend them.

If you get a chance go to your local met station, the guys there are usually very keen to show you the workings of a met station. Of relevance to this question is the location of the two therometers (wet and dry) in the white louvered box (the name of whice escapes me for the moment, any takers) which is located above the ground about 1.2 m. The box allows the therometers to read onlt the temp of the air passing through the box. The two therometers are essentialy the same as those you see hanging on thewall, ie they use mercury in a glass tube. The wet buld thermo. has a small pool of water just beneth it and a muslin ( no not the ones we are nearly at war with) or cloth suspended in the water and over the mercury resiviour of the therometer.

Of course technology is catching up, and there may some new fangled way of doing it nowdays, go and ask and let us all know.

I must admit that your threat of beers had me running to the book shelf to get the answer. But to no avail, as I don't know you and you don't (i hope) know me.

So enjoy the beers.

PS If you are real kind, just send the carton to EASTERNS care of the pilots crew room and I may get one, NOT.