. The existence of secular terms in longitude seems to be well-established for Phobos, rather uncertain for Jupiter V, and highly doubtful for Deimos. An explanation in terms of a resisting medium requires too high a space density in the case of Jupiter V and is doubtful in the case of Phobos because of the small observed effect for Deimos. The results, however, provide an upper limit of about 10-16 gm/cm3 to the space density of material near the two planets. Tidal effects are discussed briefly for Phobos and Deimos.