1. J. C. Bacri, R. Perzynski andD. Salin,Endeavour 12 (1988) 76.
2. R. E. Rosensweig in ?Ferrohydrodynamics? (Cambridge University Press, Cambridge, 1985) p. 7.
3. R. Massart, French Patent 7918842 (1979).
4. Idem., US Patent 432941 (1982).
5. Idem. 291C (1980) 1.