Abstract
THE transfer of heat across air of different densities has been examined by various experimentalists, the general result being that heat conduction is almost independent of pressure. Winkelmann (Pogg. Ann. 1875, 76) measured the velocity of cooling of a thermometer in a vessel filled with the gas to be examined. The difficulty of these experiments lies in the circumstance that the cooling is caused not only by the conduction of the gas which surrounds the cooling body, but that also the currents of the gas and, above all, radiation play an important part. Winkelmann eliminated the action of currents by altering the pressure of the gas between 760 and I millim. (with decreasing pressure the action of gas currents becomes less); and he obtained data for eliminating the action of radiation by varying the dimensions of the outer vesel. He found that, whereas a lowering of the pressure from 760 to 91.4 millims. there was a change of only 11 per cent, in the value for the velocity of cooling, on further diminution of the pressure to 47 millims. there was a further decrease of ir per cent., and this decrease continued when the pressure was further lowered, to 1.92 millim.
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On Heat Conduction in Highly Rarefied Air 1 . Nature 23, 234–235 (1881). https://doi.org/10.1038/023234a0
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DOI: https://doi.org/10.1038/023234a0