Barometer
Barometer is a class of instruments used to measure atmospheric pressure.
Mercury Barometer
The mercury barometer is very accurate and is commonly used in many weather stations. It consists of a one metre glass tube, sealed at the upper end but open at the lower end. The open end is inverted in a dish of mercury that is exposed to the air. The column of mercury will fall to about 760mm which is the normal air pressure. A rise in the column of mercury, caused by more air pressing on the mercury surface, indicates a increase in pressure while a drop shows a decrease in pressure. The air pressure is read from the scale on the tube.
Aneroid Barometer
The heart of the aneroid barometer consists of a small metal box which contains very little air. The top of this box bends slightly under the influence of any change in atmospheric pressure. The movement are transmitted by a lever system to a pointer that moves across a calibrated dial.
Barograph
The barograph consists of a metal cylinder that is partial vacuum. This corrugated cylinder moves up and down in response to pressure difference. These movements are magnified by a lever system which transmits them to a pen. The pen marks the pressure changes on a weekly chart wrapped around a revolving drum.
Altimeter
An altimeter is a modified type of aneroid barometer for aeroplanes. As pressure decreases with altitude, at an approximate rate of 25mm drop for every 270m ascent, the altimeter gives the reading in metres. Pilots uses it to tell the altitude of their planes.
Other Instruments
Other Topics
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