R.I. N¡ 276 S. MAS-GALLIC PARTICLE APPROXIMATION OF THE LINEARISED NAVIER-STOKES PROBLEM WITH NEUMANN BOUNDARY CONDITIONS The whole paper is available as a compressed Postscript file by internet procedure FTP anonymous on host barbes.polytechnique.fr ( 129.104.4.100) in the directory pub/RI/1993 under the name mas-gallic.276.mai.93.ps.gz