= Evangelista Torricelli
{c}
{title2=1608-1647}
{wiki}
<Evangelista Torricelli> interpreted the support of a <Mercury> column in terms of external <atmospheric pressure>. His 11 June 1644 letter to <Michelangelo Ricci> describes equal column heights in vessels with different upper spaces, testing whether the support came from outside the vessel. In modern <hydrostatic pressure> notation, $p_{\mathrm{atm}}-p_{\mathrm{top}}=\rho gh$, where $\rho$ is the <liquid>'s <density> and $g$ is <gravitational acceleration>. When the upper <pressure> is small, the column height measures <atmospheric pressure>, as in a <barometer>. Comparing <liquids> of different <densities> explains why <water> requires a much taller column than <Mercury>.<Letter to Michelangelo Ricci concerning the Barometer by Evangelista Torricelli>[Letter of 11 June 1644, different-vessel comparison and mercury/water height argument; modern pressure notation]{ref}
A <physicist> and <mathematician> associated here with <Torricelli's law>.https://mathshistory.st-andrews.ac.uk/Biographies/Torricelli/[Biography: 15 October 1608 to 25 October 1647; mechanics and hydrodynamics]{ref}
\Image[https://commons.wikimedia.org/wiki/Special:Redirect/file/Evangelista%20Torricelli%20by%20Lorenzo%20Lippi%20%28circa%201647%2C%20Galleria%20Silvano%20Lodi%20%26%20Due%29.jpg?width=250]
{title=Portrait of <Evangelista Torricelli>}
{description=Lorenzo Lippi (1606–1665), painting circa 1647; Galleria Silvano Lodi & Due / TEFAF. Reproduction credited in EXIF to Diego Brambilla / Studio Fotografico Perotti, 2011. https://creativecommons.org/publicdomain/mark/1.0/[PD-Art: Commons records origin-country/life-plus-100-or-shorter expiry, pre-1931 United States publication and its United States public-domain position for faithful two-dimensional reproductions.], via Wikimedia Commons.}
{source=https://commons.wikimedia.org/wiki/File:Evangelista_Torricelli_by_Lorenzo_Lippi_%28circa_1647%2C_Galleria_Silvano_Lodi_%26_Due%29.jpg}
{width=250}
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