Letter | Published:

A Ponderomotive Effect associated with the Flow of Heat through Liquid Helium II

Nature volume 142, pages 612613 (01 October 1938) | Download Citation



It has recently been suggested1,2 that liquid helium II shows a certain similarity with a Knudsen gas, the atoms moving with a very long mean free path. From the formula which is quite general (l is mean free path, χ is thermal conductivity, cν is specific heat per gram, Ï is density, ν is velocity of the atoms or quanta performing the heat conduction), one obtains values for l of several millimetres, even if one takes for χ the smallest values measured by Keesom2 and assumes for ν either the velocity of sound or a value deduced from the zero point energy (both about 2.5 × 104 cm./sec). Thus, if a Knudsen manometer were immersed in helium II, the moving vane should be repelled from the heater plate with a force of the order of magnitude where Q is the total heat flow striking the vane, provided the separation of plate and vane is less than the mean free path. Expression (2) is also of a very general nature and can only be modified by a factor of the order of magnitude of unity arising from the velocity distribution and the type of the collisions of the atoms with the vane.

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  1. 1.

    , , and de , Physica, 5, 121 (1938).

  2. 2.

    , , , and , Physica, 5, 281 (1938).

  3. 3.

    , and , NATURE, 141, 243 (1938).

  4. 4.

    , and , NATURE, 141, 74 (1938).

  5. 5.

    , NATURE, 141, 913 (1938).

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  1. H. H. Wills Physical Laboratory, University of Bristol. Aug. 26.

    • H. LONDON


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