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26

Jan

Why Does Good Weather Put Everyone Under Additional Pressure?

Written by Alex under General, Weather Station Reviews, Weather Stations | No Comments ""

Evangelista Torricelli developed the theory of atmospheric pressure in the seventeenth century. The barometer back then was not to measure air pressure but to create a vacuum above a column of water in a glass tube. After the invention of the barometer there was furious debate as to whether it could indeed be used to measure air pressure.

Aristotelians believed that air didn’t have weight and therefore couldn’t be the cause of the movement in the level of the surface of the water. If this was so then how could they explain the rise and fall of the water? Even Galileo thought that, although there were miles of air above us, it didn’t weigh down on us. Not withstanding the fact that it was he who dropped various articles from the tower at Pisa to show that gravity affected object of different weight in the same way.

Torricelli doubted that air was weightless and strove to prove that it was barometric pressure that affected the level of the water. It was his contention that it was air pressure and not the attractive force of the vacuum that affected the level of the fluid.

The fact that water would stay at thirty four feet was more reflective of the air’s pushing the water up the tube than it was with the weight of water pushing down and the vacuum it created sucking it back up. Because he saw the that the water would only rise to a certain height he saw that the barometer was in fact an instrument by which measurements could be made, rather than simply as a means to create a vacuum.

Torricelli was briefly a student of Galileo, and it was he who suggested the notion of experimenting with different liquids to see which would stop at different levels. Torricelli experimented with liquids like wine and mercury, discovering that mercury was so heavy that it found its level at a far more user friendly height than any other.

Because mercury is fourteen times more dense than water it stops rising fourteen times lower than water. If air were indeed weightless it would not impact on the height at which any fluid rose to, therefore air has weight.

Now that the experiment could be brought into a laboratory (previously experiments had to be carried out in or around high buildings) it was possible to detect slight changes in the level of the mercury from day to day. Because Torricelli knew that air had weight these changes had to be dependent on changes in weight or pressure. It wasn’t long before trends started to appear: high pressure brought good weather while low pressure bought rain, wind and higher tides.

The problem with mercury barometers was that they were filled with a toxic heavy metal, they were heavy and they couldn’t be moved easily as any spillages or leaks would ruin them.

Today it’s possible to use a Weather Station instead, these are digital devices which can sit on a shelf or desk and give you a plethora of information, including not only air pressure but humidity, interior and exterior temperature and if you have data transmitters in the green house, the garden and a cellar you can monitor them all individually.


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