Editing Barometer (section)

== History ==
[[Evangelista Torricelli]] is usually credited with inventing the barometer in 1643,<ref name="http://www.islandnet.com/~see/weather/history/barometerhistory1.htm">{{cite web|url=http://www.islandnet.com/~see/weather/history/barometerhistory1.htm |title=The Invention of the Barometer |publisher=Islandnet.com |access-date=4 February 2010 |archive-url=https://web.archive.org/web/20110514114928/http://www.islandnet.com/~see/weather/history/barometerhistory1.htm |archive-date=14 May 2011 |last=Heidorn |first=Keith C. |date=1 January 2002}}</ref><ref name="http://www.barometerfair.com/history_of_the_barometer.htm">{{cite web |url=http://www.barometerfair.com/history_of_the_barometer.htm |title=History of the Barometer |publisher=Barometerfair.com |access-date=2010-02-04 |url-status=dead |archive-url=https://web.archive.org/web/20090925023810/http://www.barometerfair.com/history_of_the_barometer.htm |archive-date=2009-09-25 }}</ref> although the historian W. E. Knowles Middleton suggests the more likely date is 1644 (when Torricelli first reported his experiments; the 1643 date was only suggested after his death).<ref name=":2" />[[Gasparo Berti]], an Italian mathematician and astronomer, also built a rudimentary water barometer sometime between 1640 and 1644, but it was not a true barometer as it was not intended to move and record variable air pressure.<ref name="http://www.islandnet.com/~see/weather/history/barometerhistory1.htm"/><ref name=":2">{{cite encyclopedia | last =Drake | first =Stillman | title =Berti, Gasparo | encyclopedia = [[Dictionary of Scientific Biography]] | volume = 2 | pages =83–84 | publisher = Charles Scribner's Sons | location = New York | year = 1970 | isbn = 978-0-684-10114-9}}</ref> French scientist and philosopher [[René Descartes]] described the design of an experiment to determine atmospheric pressure as early as 1631, but there is no evidence that he built a working barometer at that time.<ref name="http://www.islandnet.com/~see/weather/history/barometerhistory1.htm"/> In 1668, Robert Hooke's marine barometer, made by Henry Hunt, was noticed, and efforts were made to make it sea-worthy.<ref name=":3">{{Cite journal |last=McConnell |first=Anita |date=2005 |title=Origins of the Marine Barometer |journal=Annals of Science |volume=62 |issue=1 |pages=83–101 |doi=10.1080/0003379031000095767 |oclc=}}</ref>

=== Baliani's siphon experiment ===
[[File:NSRW Siphon diagram.jpg|thumb|176x176px|Siphon]]
On 27 July 1630, [[Giovanni Battista Baliani]] wrote a letter to [[Galileo Galilei]] explaining an experiment he had made in which a [[siphon]], led over a hill about 21 m high, failed to work. When the end of the siphon was opened in a reservoir, the water level in that limb would sink to about 10 m above the reservoir.<ref name=":0">{{Cite book |last=Middleton |first=W. E. Knowles. |url=http://archive.org/details/historyofbaromet00midd |title=The history of the barometer |date=1964 |publisher=Johns Hopkins Press |pages=9}}</ref> Galileo responded with an explanation of the phenomenon: he proposed that it was the power of a vacuum that held the water up, and at a certain height the amount of water simply became too much and the force could not hold any more, like a cord that can support only so much weight.<ref name=":0" /><ref name="Shea2003">{{cite book|author=Shea, William R. |title=Designing Experiments & Games of Chance: The Unconventional Science of Blaise Pascal|url=https://books.google.com/books?id=-x6B1Q5UoE4C&pg=PA21|access-date=10 October 2012|year=2003|publisher=Science History Publications|isbn=978-0-88135-376-1|pages=21–}}</ref><ref name="History of the Barometer">{{cite web|url=http://www.strange-loops.com/scibarometer.html |title=History of the Barometer |publisher=Strange-loops.com |date=2002-01-21 |access-date=2010-02-04| archive-url= https://web.archive.org/web/20100106074525/http://www.strange-loops.com/scibarometer.html| archive-date= 6 January 2010| url-status= live}}</ref> This was a restatement of the theory of ''[[Horror vacui (physics)|horror vacui]]'' ("nature abhors a vacuum"), which dates to [[Aristotle]], and which Galileo restated as ''resistenza del vacuo''.

=== Berti's vacuum experiment ===
[[File:Gasparo Berti Experiment.jpg|thumb|198x198px|Gasparo Berti's experiment]]{{Main|Gasparo Berti#Berti's vacuum experiment}}
Galileo's ideas, presented in his ''Discorsi'' (''[[Two New Sciences]]''), reached Rome in December 1638.<ref name=":1">{{Cite book |last=Middleton |first=W. E. Knowles. |url=http://archive.org/details/historyofbaromet00midd |title=The history of the barometer |date=1964 |publisher=Baltimore, Johns Hopkins Press |pages=10}}</ref> Physicists [[Gasparo Berti]] and father [[Raffaello Magiotti]] were excited by these ideas, and decided to seek a better way to attempt to produce a vacuum other than with a siphon. Magiotti devised such an experiment. Four accounts of the experiment exist, all written some years later.<ref name=":1" /> No exact date was given, but since ''Two New Sciences'' reached Rome in December 1638, and Berti died before January 2, 1644, science historian W. E. Knowles Middleton places the event to sometime between 1639 and 1643.<ref name=":1" /> Present were Berti, Magiotti, [[Society of Jesus|Jesuit]] polymath [[Athanasius Kircher]], and Jesuit physicist [[Niccolò Zucchi]].<ref name="History of the Barometer" />

In brief, Berti's experiment consisted of filling with water a long tube that had both ends plugged, then standing the tube in a basin of water. The bottom end of the tube was opened, and water that had been inside of it poured out into the basin. However, only part of the water in the tube flowed out, and the level of the water inside the tube stayed at an exact level, which happened to be {{convert|10.3|m|ft|abbr=on}},<ref>{{cite book |last=Gillispie |first=Charles Coulston |author-link1=Charles Coulston Gillispie |title=The Edge of Objectivity: An Essay in the History of Scientific Ideas |url=https://archive.org/details/edgeofobjectivit00char/page/99 |url-access=registration |year=1960 |publisher=Princeton University Press |isbn=0-691-02350-6 |pages=[https://archive.org/details/edgeofobjectivit00char/page/99 99–100] }}</ref> the same height limit Baliani had observed in the siphon. What was most important about this experiment was that the lowering water had left a space above it in the tube which had no intermediate contact with air to fill it up. This seemed to suggest the possibility of a vacuum existing in the space above the water.<ref name="History of the Barometer"/>

=== Evangelista Torricelli ===
[[File:Evangelista Torricelli by Lorenzo Lippi (circa 1647, Galleria Silvano Lodi & Due).jpg|thumb|202x202px|Evangelista Torricelli]]
Evangelista Torricelli, who was Galileo's amanuensis for the last three months of his life, interpreted the results of the experiments in a novel way. He proposed that the weight of the atmosphere, not an attracting force of the vacuum, held the water in the tube. In a letter to [[Michelangelo Ricci]] in 1644 concerning the experiments, he wrote:

<blockquote>Many have said that a vacuum does not exist, others that it does exist in spite of the repugnance of nature and with difficulty; I know of no one who has said that it exists without difficulty and without a resistance from nature. I argued thus: If there can be found a manifest cause from which the resistance can be derived which is felt if we try to make a vacuum, it seems to me foolish to try to attribute to vacuum those operations which follow evidently from some other cause; and so by making some very easy calculations, I found that the cause assigned by me (that is, the weight of the atmosphere) ought by itself alone to offer a greater resistance than it does when we try to produce a vacuum.<ref>{{cite web|url=http://web.lemoyne.edu/~giunta/torr.html |title=Torricelli's letter to Michelangelo Ricci |publisher=Web.lemoyne.edu |access-date=2010-02-04}}</ref></blockquote>

It was traditionally thought, especially by the [[Aristotelianism|Aristotelians]], that the air did not have weight; that is, that the kilometers of air above the surface of the Earth did not exert any weight on the bodies below it. Even Galileo had accepted the weightlessness of air as a simple truth. Torricelli proposed that rather than an attractive force of the vacuum sucking up water, air did indeed have weight, which pushed on the water, holding up a column of it. He argued that the level that the water stayed at—c. 10.3&nbsp;m above the water surface below—was reflective of the force of the air's weight pushing on the water in the basin, setting a limit for how far down the water level could sink in a tall, closed, water-filled tube. He viewed the barometer as a balance—an instrument for measurement—as opposed to merely an instrument for creating a vacuum, and since he was the first to view it this way, he is traditionally considered the inventor of the barometer, in the sense in which we now use the term.<ref name="History of the Barometer"/>

==== Torricelli's mercury barometer ====
[[File:Torricelli.jpg|thumb|239x239px|Torricelli's mercury in glass tube experiment]]
Because of rumors circulating in Torricelli's gossipy Italian neighborhood, which included that he was engaged in some form of sorcery or witchcraft, Torricelli realized he had to keep his experiment secret to avoid the risk of being arrested. He needed to use a liquid that was heavier than water, and from his previous association and suggestions by Galileo, he deduced that by using [[Mercury (element)|mercury]], a shorter tube could be used. With mercury, which is about 14 times denser than water, a tube only 80&nbsp;cm was now needed, not 10.5&nbsp;m.<ref>{{cite web|url=http://www.barometer.ws/history.html |title=Brief History of the Barometer |publisher=Barometer.ws |access-date=2010-02-04| archive-url= https://web.archive.org/web/20100114144734/http://www.barometer.ws/history.html| archive-date= 14 January 2010 | url-status= live}}</ref> Furthermore, Torricelli demonstrated that atmospheric pressure could support a column of mercury approximately 30 inches high.<ref>{{Cite journal |title=1944JRASC..38...41K Page 49 |url=https://articles.adsabs.harvard.edu//full/1944JRASC..38...41K/0000049.000.html |access-date=2025-03-07 |journal=Journal of the Royal Astronomical Society of Canada|bibcode=1944JRASC..38...41K |last1=Knowles Middleton |first1=W. E. |date=1944 |volume=38 |page=41 }}</ref>

=== Blaise Pascal ===
[[File:Portrait de Blaise Pascal (MARQ 999.3.1).jpg|left|thumb|178x178px|Blaise Pascal]]
In 1646, [[Blaise Pascal]] along with [[Pierre Petit (engineer)|Pierre Petit]], had repeated and perfected Torricelli's experiment after hearing about it from [[Marin Mersenne]], who himself had been shown the experiment by Torricelli toward the end of 1644. Pascal further devised an experiment to test the Aristotelian proposition that it was vapours from the liquid that filled the space in a barometer. His experiment compared water with wine, and since the latter was considered more "spiritous", the Aristotelians expected the wine to stand lower (since more vapours would mean more pushing down on the liquid column). Pascal performed the experiment publicly, inviting the Aristotelians to predict the outcome beforehand. The Aristotelians predicted the wine would stand lower. It did not.<ref name="History of the Barometer" />

==== First atmospheric pressure vs. altitude experiment ====
{{Main|Blaise Pascal#First atmospheric pressure vs. altitude experiment}}
[[File:Puy de dome, May 2012.jpg|thumb|Puy de Dôme]]
[[File:Florin Périer measuring the mercury level in a Torricelli barometer near the top of the Puy de Dôme.jpg|alt=Florin Périer measuring the mercury level in a Torricelli barometer near the top of the Puy de Dôme|thumb|Florin Périer on the Puy de Dôme]]
However, Pascal went even further to test the mechanical theory. If, as suspected by mechanical philosophers like Torricelli and Pascal, air had weight, the pressure would be less at higher altitudes. Therefore, Pascal wrote to his brother-in-law, Florin Perier, who lived near a mountain called the [[Puy de Dôme]], asking him to perform a crucial experiment. Perier was to take a barometer up the Puy de Dôme and make measurements along the way of the height of the column of mercury. He was then to compare it to measurements taken at the foot of the mountain to see if those measurements taken higher up were in fact smaller. In September 1648, Perier carefully and meticulously carried out the experiment, and found that Pascal's predictions had been correct. The column of mercury stood lower as the barometer was carried to a higher altitude.<ref name="History of the Barometer" />