The introduction of triplet potentials into the Percus-Yevick theory of fluids

The introduction of triplet potentials into the Percus-Yevick theory of fluids is made by a method similar to that of Rushbrooke and Silbert, but based upon a different classification of the graphs in the expansion of the correlation function. Their method is suitable for the hyper-netted chain theory but, it is suggested, the method used here is more appropriate for the Percus-Yevick theory. The results differ, and are compared.