The words of this preface were written when the book was ready to go to
the press; and are limited to only a few points which are best made in
this place. As is intimated by the sub-title, the whole volume was
written with appli- cations in mind to double-star astronomy. The latter
is, however, not the only branch of our science which could benefit from
its contents. The same is true of certain aspects of the dynamics of
stellar systems or galaxies (the stellar popula- tions of which are also
characterized by the fact that the mean-free-path of their constituent
stars are long in comparison with the dimensions of the respective
systems); the central condensations of which are high enough to
approximate the gravitational action of a "mass-point". This fact did
not, to be sure, escape the attention of previous investigators (in the
case of globular clusters, in particular, the Roche model was introduced
in their studies under the guise of polytropic models characterized by
the index n = 5); though no particular attention will be paid to these
in this book. But possible applications of the Roche model are not
limited to problems arising in stellar astrophysics. With Coulomb forces
replacing gravitation, the equilibrium model finds a close analogy in
the field of electrostatics-as was pointed out already at the beginning
of this century by (then young) J. H. Jeans (cf.