Barometric pressure is the pressure or force that the atmosphere exerts on the world around it. Barometric pressure is variable and changes with weather, temperature and altitude.
The atmosphere is largely made up of oxygen and nitrogen, which have mass, albeit a very small mass. This mass exerts pressure known as barometric pressure. At sea level, due to the Earth's gravity, the atmosphere is much thicker and denser than at a higher altitude.
Gravity causes the gases to be pulled to the surface of the Earth. The closer an object (even gases such as nitrogen and oxygen) is to the Earth, the greater the effect. The converse is also true; that is, the further an object is from the surface of the earth the less effect gravity has on the object. Therefore, at a lower altitude the barometric pressure will be greater than the barometric pressure at a higher altitude.
The planet Venus (second planet from the sun) has a much thicker and denser atmosphere than the Earth's. At surface level, the pressure is so great that it would flatten a human being and crush a car.
In the 17th century, Evangelista Torricelli was the first scientist to create the barometer to measure air pressure. Torricelli also improved the telescope and developed the fundamental principles of hydrolics.
