The force exerted by gases in the atmosphere on some area or body on the earths surface. Measured using barometers of three types namely mercury, aneroid and Fortin Barometers
Table of Contents
How It Works
- Air exerts pressure on the mercury in the beaker.
- The height of mercury in the tube is proportional to the atmospheric pressure.
- The readings are taken in mmHg.
- Its 760mmHg at sea level
Advantage
Quite accurate
Disadvantage
- Cumbersome to carry around.
- Can be damaged quite easily while being carried around.
Aneroid Barometer
-Measures changes in atmospheric pressure.
How It Works
- Has air tight compartment (vacuum).
- Compartment expands when pressure decreases.
- It collapses when pressure increases.
- The movement is transmitted by lever to a pointer on a dial.
- The readings are in kg/cm3.
Evaporation
The rate and amount of evaporation is measured using piche and tank evaporimeters.
Piche Evaporimeter
- When there is a lot of sunshine water evaporates from the blotting paper.
- The level of water in the glass tube reduces.
- The rate and amount of evaporation is got by looking at the scale on the outside of the glass tube.
- The units are in mm.
Tank Evaporimeter
How It Works
- The tank with water is put in the open.
- Water evaporates when there is a lot of sunshine.
- Water in the tank reduces.
- The rate and amount of evaporation is got from calibrations in the inner side of the tank in mm.
Cloud Cover
The amount of cloud cover is observed using eyes.
It’s given in oktas.
Okta=approximately 1/8 of sky is covered with clouds.