Notes on the Barometer

I have been fascinated by the weather since early childhood.

I have also had a keen interest in sciences of all kinds, throughout my life though I am not very good at it. I mean I am so terrible at science that I don’t even hold an Associate’s Degree.

However, I do spend a good bit of my time engaged in independent learning.

In this page, I will post the transcript of notes I had taken in my composition book that detail information about Barometers.

Without further ado, here they are:

These notes were taken on October 1st and 2nd of 2018.

The main reference that I will cite is Wikipedia as that is where I got the bulk of this material from.

Notes on the barometer and its inventor(s).

Barometers are used in meteorology to measure atmospheric pressure.

Pressure tendency detects short term changes in weather.

Measuring air pressure within surface weather analysis is helpful in locating surface troughs, high-pressure systems and frontal boundaries.

The term “barometer is derived from ancient Greek words which literally translate into words that mean weight and meter/measure.

Evangelista Torricelli (October 15, 1608-October 25, 1647) an Italian physicist and mathematician are credited with inventing the barometer in 1643.

Italian astronomer and mathematician Gapardo Berti (1600-1643) may have also unintentionally created a water barometer sometime between 1640 and 1643.

French scientist and philosopher Rene` Descartes (March 31, 1596-February 11, 1650) described the design of an experiment to measure air pressure possibly as early as 1631 but no evidence is there to suggest that he actually built such an instrument.

On July 27, 1630, Italian mathematician, physicist and astronomer Giovanni Battista Baliania (1582-1666) wrote to Italian polymath Galileo Galilei (February 15, 1564-January 8, 1642) describing a failed experiment in which he made a siphon led over a hill ~21 meters high. Galileo replied explaining that the power of the vacuum held the water up but at a certain height the amount of water was simply too much and the vacuum could not hold anymore, like a cord that can only support so much weight. This was a restatement of “horror vacui” or “nature abhors a vacuum, a theory which dates back to ancient Greek philosopher and scientist, Aristotle (384-322 BC.) Galielo restated this theory as “resistenza del vacuo.”

These theories were published in Galileo’s “Discoursi” and they reached Rome in 1638.

Raffade Magiotti and Berti were excited by these ideas and sought another way to produce a vacuum besides a siphon.

Magiotti devised the experiment and Berti carried it out sometime between 1639 and 1641.

A simple model of this experiment consisted of filling a long tube with water plugged on both ends, then stood up in a water-filled basin. The bottom plug was removed and the water inside the tube flowed into the basin. However, only a portion of the water flowed out of the tube and the height of the water inside the tube stayed at an exact level, which happened to be 10.3 meters or 34 feet, the same height that Galileo and Baliani observed to be limited by the siphon.

The most important detail of this experiment was that lowering the water in the tube left a space above it in the tube with no immediate contact with air. This suggested the possibility of a vacuum existing in the space above the water.

Torricelli, a pupil, and friend of Galileo interpreted the results of this in a novel way. He proposed that it was the atmosphere and not the attracting force of the vacuum that held the water in the tube.

Followers of Aristotle and Galileo thought air to be weightless.

Torricelli questioned and challenged this belief and suggested that air indeed has weight and it was the weight of the air which pushed up and held the column of water.

Torricelli believed that the level of which the water stayed at in the tube (10.3 meters of 34 feet) was reflective of the air’s weight pushing on the water in the basin, thus limiting how much water can fall from the tube into the basin.

Torricelli viewed the barometer as a balance or measuring instrument instead of a device to merely build a vacuum.

Because pf Torricelli being the first to observe this, he is credited as being the inventor of the barometer.

Torricelli’s gossipy Italian neighbors spread rumors that he was engaging in sorcery and witchcraft. Torricelli thus decided to keep his experiments a secret to avoid being arrested by the Roman Catholic Church.

In order to be more covert, he needed a liquid denser than water, to which Galileo suggested he use Mercury. As a result, he only needed a tube that was 80 centimeters long as opposed to 10.5 meters.

*SIDE NOTE*: While I was initially taking these notes on that evening in early October 2018, I decided to take a few sips of Wild Cherry Pepsi in an attempt to temper the sting of depression which I frequently suffer. Soft drinks, while extremely addictive do indeed help me write better and they do help fight depression, at least for me. Wild Cherry Pepsi is my favorite soft drink.

Decreasing atmospheric pressure was initially postulated by French physicist Lucien Vidi (1805-April, 1866.) He later invented the barograph, a device which records the pressure readings of an aneroid barometer.

German writer and polymath Johan Wolfgang Von Goethe (August 28, 1749-March, 22 1832) invented a water driven barometer based on Torricelli’s principles. It is known as the weather ball barometer and is comprised of a glass container with a sealed body half-filled with water. The narrow spout is open to the atmosphere. When the pressure is lower than it was at the time the body was sealed, the level of water in the spout will rise above the water level in the body. When the pressure is higher, the water level in the spout will drop below the water level in the body. This device is known as a “weather glass” or a “Goethe Barometer.

Mercury Barometer:
A vertical glass tube closed at the top sitting in an open Mercury filled basin at the bottom. The Mercury’s weight creates a vacuum at the top known as a “Torricelli Vacuum.” The Mercury in the tube fluctuates until the weight of the Mercury column balances the force of the air pressure bearing down on the reservoir. Higher temperature levels around the instrument will reduce the density of the Mercury, thus the scale must be calibrated in such a way to compensate for this effect. The tube must be as long as the amount of Mercury in addition to the headspace as well as the maximum length of the column.

Torricelli observed slight changes each day in the height of Mercury in the tube and concluded that this was due to changing pressure in the atmosphere.

On December 5, 1660, German scientist, inventor and politician Otto von Guerricke (November 20, 1602-May 11, 1686) observed that the air pressure was unusually low and predicted a storm which struck the next day.

The Mercury barometer’s design made the expression of atmospheric pressure in inches of Mercury popular. The range is typically between 26.5 and 31.5 inches (670-800 millimeters) of Mercury.

One atmosphere is equivalent to 29.92 inches or 760 millimeters of Mercury.

On June 5, 2007, the governments of the European Union restricted the sale of Mercury, effectively ending the manufacture of new Mercury barometers in Europe.

An aneroid barometer uses a flexible metal box instead of any liquid to measure air pressure. It was invented in 1844 by Lucien Vidi. The box is known as an aneroid cell or capsule made from an alloy of Beryllium and Copper.

The evacuated capsules are many times several stacked together to add movement and are protected from collapsing by a strong spring. Any change in the surrounding air pressure causes the capsule to expand or contract.

This movement drives mechanical levers in such a way that their changes are amplified and displayed on the dial face of the instrument. Many models also feature a manually set needle to mark the current observation and compare with previous and future observations so a change can be seen.

Microelectromechanical systems (MEMS) barometers are extremely small ranging size between 1 and 100 micrometers. They are manufactured using photolithography or photochemical machining. These can be found in miniature weather stations, electronic barometers, and altimeters.

Certain smartphones such as the Samsung Galaxy Nexus, Samsung Galaxy S3 through S6, the Motorola Xoom, Apple iPhone 6 as well as higher end Casio and Timex watches have built-in barometers using MEMS technology.

Formulas:
Pressure in atmospheres Patm=p*g*h
Where p=density of Mercury=13,595 kg/meter cubed (sorry I don’t know how to do sub and superscript on here) g=graviation accelaration=9.807 meters per second squared, h=height.
1 torr=133.3 Pascals or 0.03937 inches of Mercury.

My personal commentary:
Most weather predictions for civilians are obtained through the mass media and government run forecasting services. Should our enemies hit us with an EMP all of this will come to a grinding halt.

Personal maybe even homemade barometers may make a comeback should this happen.

After all, we would still want to know when will storms be headed in our area so we can spend time cuddling with bae.

A barometer could possibly give some advanced notice of incoming foul weather.

However, all modern conveniences will be gone so will we actually have the time to cuddle with bae?

The weather might be the least of our worries as I’ve stated before and cuddling with bae might be highly frowned upon because cuddling sometimes leads to intercourse and intercourse ultimately means more hungry mouths to feed…

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