# How atmospheric humidity is measured

#### halfdyke

it is not a myth that on some days our hair seems to not want to cooperate with whatever style we've chosen (this is especially true for women's hair styles). meteorologists use an instrument known as a hair hygrometer to measure the humidity in the atmosphere, because human hair has been found to be extremely sensitive to humidity.

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#### sheldon

Yes your right, if that is a question or statement I am unsure, I agree either way.

#### russ_watters

Mentor
Another way is with a psychrometer - a wet and dry thermometer.

#### russ_watters

Mentor
Originally posted by sheldon
then you would have to use a psycrometric chart.
Well, it depends on your job. I'm an HVAC engineer, so I use the psyc chart.

#### STAii

Once at school, i a new way to calculate humidity came up to my ming (well, it might not be new, but i never saw it in any book !). Btw, it also might be not really accurate.
1-Get a can of iron.
2-Fill it with ice, put a thermometer inside it.
3-As soon as u see drops of water on the outer surface of the can, look at the temprature that the thermometer is telling.
4-The temprature that u have just taken is the temprature at which the humidity of air round the can became 100%.
5-Use charts to know the saturation of air at that temprature. (call it S1)
6-Take the temprature of the place, away from the can.
7-Use charts again to know the saturation of air at this temprature. (call it S2)
Now simply, the humidity is (S1/S2)*100%

Is my idea right ?

#### russ_watters

Mentor
Originally posted by STAii
Is my idea right ?
Except for two things - you need the surface temperature of the outside of the can. Also, you don't need to do the calculation - the psyc chart has all sorts of info about air at a given set of conditions. But yes, that will work.

#### sheldon

Originally posted by STAii
Once at school, i a new way to calculate humidity came up to my ming (well, it might not be new, but i never saw it in any book !). Btw, it also might be not really accurate.
1-Get a can of iron.
2-Fill it with ice, put a thermometer inside it.
3-As soon as u see drops of water on the outer surface of the can, look at the temprature that the thermometer is telling.
4-The temprature that u have just taken is the temprature at which the humidity of air round the can became 100%.
5-Use charts to know the saturation of air at that temprature. (call it S1)
6-Take the temprature of the place, away from the can.
7-Use charts again to know the saturation of air at this temprature. (call it S2)
Now simply, the humidity is (S1/S2)*100%

Is my idea right ?
I am unsure of this, But the thermometer should read 32 degree's untill it is completely melted even so you have the cup filled with iron. You can check a thermometers accuracy this way. A cup of ice water is always 32 degree's. I suppose that as the iron cools its thermal conductive properties would help change the temp of the ouside of the can. Yes the more I think about what your doing the more I believe it will work. Thats neat I will have to try it.

When the weatherman says "humidity is 35%", he means the air has 35% of the water it can hold at whatever temperature it is. Humidity is just that: a measure of the water content of the air at whatever temp. Wow, looky here: http://chemistry.about.com/library/glossary/bldef7620.htm

#### Artman

You can also buy electronic psycrometric sensors that can give a fairly accurate reading of the relative humidity much faster and easier than a sling psychrometer (although possibly not as accurately).

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