The document discusses barometers, which are tools used to measure atmospheric pressure. It describes the basic types of barometers, including mercury barometers and aneroid barometers. It explains how barometers can be used to predict weather changes by measuring fluctuations in air pressure. Specifically, decreasing pressure typically signifies stormy weather, while rising pressure usually means calm conditions. The document also outlines some common applications of barometers in weather forecasting.

1. BAROMETER Engr. Rudy U. Panganiban

2. OUTLINE 1. Facts about Barometer
2. Interesting Barometer Facts
3. Types of Barometer
4. Applications
5. How does Barometer predict weather

3. FACTS ABOUT BAROMETER
A barometer is a meteorological tool used to measure
atmospheric pressure. Measuring pressure in the
atmosphere can help to forecast weather changes in
the short term. The barometer was invented either by
Gasparo Berti in the 1640s or Evangelista Torricelli in
1643. Barometers and pressure altimeters are
essentially the same tool but barometers are kept
stationary to measure atmospheric pressure and
pressure altimeters are moved around from one place
to another and matched to altitude. Atmospheric
pressure it the weight of the air in the atmosphere
and the barometer is able to measure this, which
makes it one of a weather station's basic sensors and
tools.

4. INTERESTING BAROMETER FACTS
The two main types of barometers used for meteorology
(weather science) are the aneroid barometer and the mercury
barometer.
A mercury barometer is usually a three foot high glass tube
closed at one end with a reservoir of mercury open at the other.
Atmospheric pressure changes the level of the mercury in the
column.
An aneroid barometer is a barometer without liquid, invented by
Lucien Vidi in 1844. An aneroid cell in the barometer expands or
contracts as a result of changes in external air pressure.
The main types of barometers are water-based barometers,
mercury barometers, vacuum pump oil barometers, aneroid
barometers, and barographs.
More unusual types of barometers include Collins Patent Table
Barometer, Hooke's Otheometer, Ross Sympiesometer and the
Shark Oil barometer,
Some cell phones have aneroid barometers built in, such as the
iPhone 6 smartphone, the Samsung Galaxy S3 to S6 models, and
the Galaxy Nexus. The aneroid barometer does not use mercury.

5. Barometers have been used in weather forecasting dating back
to the late 1800s.
Altitude plays a role in the accuracy of a barometric reading.
Because boats are at sea level they are the exception to using
barometers in a fixed location.
High pressure occurs when the air sinks to the earth more
quickly than it is able to flow outward. With a mercury
barometer this causes the mercury to rise higher and gives a
reading of high pressure.
Low pressure occurs when air rises from the earth more quickly
than air flow is able to replace the lost air. With a mercury
barometer the mercury drops to a lower level and gives a
reading of low pressure.
Although mercury barometers are accurate they contain mercury
- which is not safe because it is a very poisonous form of liquid
metal. The aneroid barometer was created to make barometers
safer for use. Aneroid barometers are commonly used in small
aircraft and in homes, as well as boats, or other places where
mercury is not safe.

6. Barometric pressure can be reported in several different
measurement units including in Hg(mercury) (inches of mercury
- used mostly in the U.S.), mb (millibars - commonly used by
meteorologists), Pa (pascals - worldwide SI unit of pressure), and
Atm (atmospheres- pressure of air at sea level when
temperature is 59 degrees Fahrenheit).
When used for weather forecasting, decreasing air pressure
usually is a sign of stormy, windy or rainy weather while slow
rising air temperature is a sign of dry, calm weather.

7. • Types of the Barometer
Its two main types are as follows:
1. Mercury Barometer
2. Aneroid Barometer

8. Mercury barometer
This is the most popular barometer. It consists of the glass
column with mercury and markings of inches on it. Its top
end is closed and the bottom end is rested in the cup
having mercury i.e. cistern. For more accuracy, these
barometers are corrected for the ambient temperature
gravity. This mercury is in use because of its density.
Aneroid barometer
This barometer comprises of fluid. It consists of the
aneroid capsule which is a thin and flexible alloy based
metal box This alloy is of beryllium and copper. For better
expansion and contraction of the levers and springs of
box happening due to change in the atmospheric
outside the box, the box is tightly sealed.

9. APPLICATIONS
Barometric pressure and the pressure tendency (the change of
over time) have been used in weather forecasting since the late 19th
century. When used in combination with wind observations,
accurate short-term forecasts can be made. Simultaneous barometric
readings from across a network of weather stations allow maps of air
pressure to be produced, which were the first form of the
modern weather map when created in the 19th century. Isobars, lines
equal pressure, when drawn on such a map, give a contour map
showing areas of high and low pressure. Localized high atmospheric
pressure acts as a barrier to approaching weather systems, diverting
their course. Atmospheric lift caused by low-level wind convergence
into the surface brings clouds and sometimes precipitation. The larger
the change in pressure, especially if more than 3.5 hPa (0.1 inHg), the
greater the change in weather that can be expected. If the pressure
drop is rapid, a low pressure system is approaching, and there is a
greater chance of rain. Rapid pressure rises, such as in the wake of
a cold front, are associated with improving weather conditions, such as
clearing skies.

10. • How does Barometer Predict Weather
The basic rules of thumb are: If the barometer measures low air
pressure, the weather is bad; if high pressure, it is good. If
pressure is falling, then the weather will get worse; if rising,
better. The faster it is falling or rising, the faster and more the
weather will change.