The method of integrating the differential equations of motion, adopted by DELAUNAY for the elaboration of his lunar theory, as it is explained by him, demands its division into several cases, and is established through very tedious transformations. These disadvantages disappear when the greatest generality is given to the procedure. Hence, an explanation of the method, as it would be applied to the motion of a planetary system like the solar, will, doubtless, be welconme to astronomers.
G. W. Hill (Mon,) studied this question.