4 : Barometer and Altimeter

Question 1

• an instrument for measuring variations in atmospheric pressure
• first barometer was the device by Evangelista Torricelli

Answer 1

Barometer

Question 2

• measures atmospheric pressure by the height of a column of mercury supported by the atmosphere in an evacuated glass tube
• under standard conditions, the mercury column is about 76 cm high at sea level
• a centimeter in the height of the mercury column corresponds to a difference of about 108 m in altitude
• standard atmospheric pressure at sea level: 1013.2 millibars

Answer 2

Mercurial Barometer

Question 3

• invented by Lucien Vidie of France
• functions by using an airtight metal box which responds to changes in air pressure

Answer 3

Aneroid Barometer

Question 4

• precise aneroid barometers designed specifically for surveying applications

Answer 4

Altimeter

Question 5

• in this method, two altimeters and two thermometers are employed
• one altimeter remains at a reference base whose elevation is known while the other altimeter (roving altimeter) is taken to other points or field stations whose elevations are to be determined

Answer 5

Single-Base Method

Question 6

• designed to eliminate the need to apply correctness for the effects of temperature and relative humidity
• one base is established at a suitable low point (lower base) while a second base is positioned at a much higher elevation (upper base)

Answer 6

Two-Based Method