1. Thomson, W., Pap. Electrostat. and Magnetism, 1872, p. 564.
2. Stefan, J., Ann. Phys. Lpz.38 (1889) 440.
3. Bates, L.F., Modern Magnetism, third edition, Cambridge 1951, p. 77.
4. Bitter, F., Rev. Sci. Instrum.7 (1936) 479.
5. De Klerk, D., Ned. T. Natuurkde26 (1960) 1.