Dear Sirs, The comm~nicat~un by Hartman et al. (1989) presents a new correlation for calculating the terminal falling velocity of spherical particles. This is of great interest because such correlations are at the basis of many a design proozdun for particle separators, be it for removal of solids or finely dispersed liquids. Given the present-day emphasis on the protection of our environment, any improvement in the separator design is certainly welcome. However> even with all due regard to the effort which must have gone into deriving the new formula, eqs tS)+3c), X find its presentation unnecessarily complex. Noting that eq. (8a) contains a decadic logatitbm which then appears in the exponent of base 10 in eq.(lf) and that one term in the argument of the sine function in eq. (8b) is close to n, I propose that eqs (Sf-iSb) be replaced with where all symbols are the same as in the original cammunication. For a frequent computational use one might also replace the decadic logarithm with a natural one, B = In <A$: Re, = CO.05464 -0.001013 RRFBXtRNCE Hartman, M., Wavlin, V., Tmka, 0. and &Brsk$, M., 1989, Predicting the free-fait velocities of spheres. Chem. Engng