$n(n+1\mathrm{})/2\mathrm{}$ independent diffraction measurements are needed to obtain complete partial structure information for a disordered n-component condensed system. A previous assertion that only n of these are independent is shown to be inapplicable, for different reasons, to both the three-dimensional partial structure factors $S_{\mathrm{ab}}\left(\mathbf{Q}\right)$ and the orientational averages $S_{\mathrm{ab}}\mathrm{}\left(Q\right).$ The fluctuations of $S_{\mathrm{ab}}\left(\mathbf{Q}\right)$ about $S_{\mathrm{ab}}\mathrm{}\left(Q\right)\mathrm{}$ and the effects of thermal motion are discussed.

• Received 24 August 1998

DOI:https://doi.org/10.1103/PhysRevB.59.5