1. Nature 141, 1938.
2. Kurt Mendelssohn, The Quest for Absolute Zero, Taylor & Francis Ltd., 2nd Ed., London 1977, p. 246.
3. A. Eisner, G. Klipping, Control System for Temperatures and liquid level between 4.2° and 1° K, in: “Advances in Cryogenic Engineering”, Vol. 14, Plenum Press, New York 1969, p. 416.
4. A. Eisner, Helium Flow through Filters, in “Advances in Cryogenic Engineering”, Vol. 16, Plenum Press, New York 1973, p. 141.
5. M.R. Bennett, D.S. Brown, D.B.A. Macmichael, R.J. Mytton, H. Prokuro, J.S.H. Ross, M. Sheenan, R. Wand, “Study of the Technological Requirements Associated with a Space Infra-Red Astronomy Survey”, Research Rept. IRD 74/52-ESRO C.R. (P)-568 (1974).