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Pitch Pool

K.M.I.5. (Green and Lloyd catalogue number in white paint). DES THOMSON,William,Lord,1st Baron Kelvin of Largs. circa 1882 Glasgow, Scotland. MANU THOMSON,William,Lord,1st Baron Kelvin of Largs. circa 1882 Glasgow, Scotland. This experiment was used to show that small persistently applied forces are sufficient to produce unlimited changes in the shape of a substance over long periods of time. Kelvin used this model to show that it was possible for a homogeneous material to possess properties similar to the properties that he needed to assign to the luminiferous ether.

The pitch pool was devised for his Baltimore Lectures in 1884 and has been repeated many times. It relies on two seemingly mutually exclusive properties of Scotch cobbler's wax that mimic Kelvin?s ether. The wax, when dropped onto a hard surface will shatter like glass, demonstrating inelasticity. However, it will slowly flow like a viscous liquid under the influence of a persistent force such as gravity.