Editing Blaise Pascal (section)

=== First atmospheric pressure vs. altitude experiment ===
[[File:Puy de Dôme near Clermont-Ferrand in Auvergne in France.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]]

The [[Torricellian vacuum]] found that air pressure is equal to the weight of 30 inches of mercury. If air has a finite weight, Earth's atmosphere must have a maximum height. Pascal reasoned that if true, air pressure on a high mountain must be less than at a lower altitude. He lived near the [[Puy de Dôme]] mountain, {{convert|4790|ft}} tall, but his health was poor so could not climb it.<ref name="ley196606">{{Cite magazine
 |last=Ley
 |first=Willy
 |date=June 1966
 |title=The Re-Designed Solar System
 |department=For Your Information
 |url=https://archive.org/stream/Galaxy_v24n05_1966-06#page/n93/mode/2up
 |magazine=Galaxy Science Fiction
 |pages=94–106
}}</ref> On 19 September 1648, after many months of Pascal's friendly but insistent prodding, [[Florin Périer]], husband of Pascal's elder sister Gilberte, was finally able to carry out the fact-finding mission vital to Pascal's theory. The account, written by Périer, reads:

{{blockquote|The weather was chancy last Saturday...[but] around five o'clock that morning...the Puy-de-Dôme was visible...so I decided to give it a try. Several important people of the city of [[Clermont-Ferrand|Clermont]] had asked me to let them know when I would make the ascent...I was delighted to have them with me in this great work...

...at eight o'clock we met in the gardens of the Minim Fathers, which has the lowest elevation in town....First I poured 16 pounds of [[Mercury (element)|quicksilver]]...into a vessel...then took several glass tubes...each four feet long and [[Hermetic seal|hermetically sealed]] at one end and opened at the other...then placed them in the vessel [of quicksilver]...I found the quick silver stood at 26" and {{frac|3|1|2}} lines above the quicksilver in the vessel...I repeated the experiment two more times while standing in the same spot...[they] produced the same result each time...

I attached one of the tubes to the vessel and marked the height of the quicksilver and...asked Father Chastin, one of the Minim Brothers...to watch if any changes should occur through the day...Taking the other tube and a portion of the quick silver...I walked to the top of Puy-de-Dôme, about 500 [[fathoms]] higher than the monastery, where upon experiment...found that the quicksilver reached a height of only 23" and 2 lines...I repeated the experiment five times with care...each at different points on the summit...found the same height of quicksilver...in each case...<ref>Périer to Pascal, 22 September 1648, Pascal, Blaise. ''Oeuvres complètes''. (Paris: Seuil, 1960), 2:682.</ref>}}

Pascal replicated the experiment in Paris by carrying a barometer up to the top of the bell tower at the church of [[Saint-Jacques Tower|Saint-Jacques-de-la-Boucherie]], a height of about 50 metres. The mercury dropped two lines. He found with both experiments that an ascent of 7 fathoms lowers the mercury by half a line.{{efn|1=1 ligne = 2.256 mm, and 1 toise = 1.949 m. Mercury density is 13.534 g/cm3. So by Pascal's numbers, the density of air is about 1.1 kg/m<sup>3</sup>.}} Note: Pascal used [[Units of measurement in France before the French Revolution#Length|''pouce'' and ''ligne'']] for "inch" and "line", and ''[[toise]]'' for "fathom".<ref>{{Cite journal |last=Rougier |first=Louis |date=2010-10-01 |title=– Chapitre XI – La Grande expérience de l'équilibre des liqueurs |journal=Philosophia Scientiæ. Travaux d'histoire et de philosophie des sciences |volume=14-2 |language=fr |issue=14–2 |pages=196–206 |doi=10.4000/philosophiascientiae.189 |issn=1281-2463 |doi-access=free }}</ref>

In a reply to [[Étienne Noël]], who believed in the plenum, Pascal wrote, echoing contemporary notions of science and [[falsifiability]]: "In order to show that a hypothesis is evident, it does not suffice that all the phenomena follow from it; instead, if it leads to something contrary to a single one of the phenomena, that suffices to establish its falsity."<ref>''Pour faire qu'une hypothèse soit évidente, il ne suffit pas que tous les phénomènes s'en ensuivent, au lieu que, s'il s'ensuit quelque chose de contraire à un seul des phénomènes, cela suffit pour assurer de sa fausseté'', in ''Les Lettres de Blaise Pascal: Accompagnées de Lettres de ses Correspondants Publiées'', ed. Maurice Beaufreton, 6th edition (Paris: G. Crès, 1922), 25–26, available at http://gallica.bnf.fr {{Webarchive|url=https://web.archive.org/web/20161218172021/http://gallica.bnf.fr/ |date=18 December 2016 }} and translated in Saul Fisher, ''Pierre Gassendi's Philosophy and Science: Atomism for Empiricists'' Brill's Studies in Intellectual History 131 (Leiden: E. J. Brill, 2005), 126 n.7</ref>

[[Blaise Pascal Chair]]s are given to outstanding international scientists to conduct their research in the [[Île-de-France (region)|Ile de France]] region.<ref>{{cite web|title=Chaires Blaise Pascal|url=http://www.chaires-blaise-pascal.org/uk/index.html|url-status=dead|archive-url=https://web.archive.org/web/20090613064029/http://www.chaires-blaise-pascal.org/uk/index.html|archive-date=13 June 2009|access-date=16 August 2009|publisher=Chaires Blaise Pascal}}</ref>