Page 145 - English Class 9

technology which includes different weather instruments and weather
stations that help us to accumulate accurate weather data. There are
different types of instruments for measuring different parameters.

A THERMOMETER is a device that is used for measuring the temperature
or the temperature gradient. This can be used in industry, in meteorology,
and even in medicine. This device has two important things that help in
measuring the temperature. The first one is a sensor that uses different
physical parameters like the expansion of different states of matter for
sensing the change. The second one is a converter that converts the change
of temperature into a numerical number.

There are different types of thermometers. In weather stations, mainly
mercury-filled thermometers are used. Mercury-filled thermometers can
measure the temperature from -35 to 40 degree Celsius. It has a scale
division of 0.2 degrees. But if the temperature is less than -35 degree
Celsius, then this thermometer cannot give an accurate result and
becomes unreliable. To measure the temperature under -35 degree Celsius,
alcohol-filled thermometers are used. This type of thermometer can
measure from -65/-75 degree Celsius to 20/25 degree Celsius.

A BAROMETER is an instrument that measures
the atmospheric pressure. It measures pressure in
measurement units called bars or atmospheres. The
earth is wrapped with layers of air which is called
atmosphere. The air has weight, and it presses everything
against gravity. A barometer measures this pressure.
When a barometer shows low-pressure, it means that
the weather is rainy, windy or cloudy and when the pressure is high, it
means that the weather is fair.

There are different types of barometer such as the mercury
barometer, aneroid barometer, and the digital barometer.
Among these three, the digital barometer is the latest one
that gives more accurate data.

A HYGROMETER measures the humidity or the amount
of water vapour in the air. There are mainly two types of hygrometers.
They are dry and wet bulb hygrometers and a mechanical hygrometer.

AN ANEMOMETER is used to measure the speed of the wind. The
English 9 139