= August Kundt
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{title2=1839–1894}
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<August Kundt> made <standing wave> patterns of <sound waves> visible through the dust patterns in <Kundt's tube>. Neighboring repeat marks in the ideal pattern are separated by half a <wavelength>, so a measured spacing $d$ and known <frequency> $f$ give <speed of sound> $c=2fd$. The tube turns an oscillation too rapid to follow directly into a spatial ruler. Comparing resonance conditions in a solid rod and a gas also connects the method with measurements of sound propagation in different materials.<Ueber eine neue Art akustischer Staubfiguren und über die Anwendung derselben zur Bestimmung der Schallgeschwindigkeit in festen Körpern und Gasen by August Kundt>[1866 paper, acoustic dust figures and sound-speed measurements]{ref}
A <physicist> whose appointments took him from Zürich in 1868 through Würzburg and Strasbourg to the Berlin chair of experimental physics in 1888.<August Kundt by Berlin-Brandenburgische Akademie der Wissenschaften>[Kurzbiographie: physics professorships and life dates]{ref}
\Image[https://upload.wikimedia.org/wikipedia/commons/2/27/August_Kundt-1893-1894.png]
{title=Portrait of <August Kundt>}
{source=https://commons.wikimedia.org/wiki/File:August_Kundt-1893-1894.png}
{width=240}
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