Seneca’s _Natural Questions_—Nature study as an ethical substitute for existing religion—Limited field of Seneca’s work—Marvels accepted, questioned, or denied—Belief in natural divination and astrology—Divination from thunder—Ptolemy—His two chief works—His mathematical method—Attitude towards authority and observation—The _Optics_—Medieval translations of _Almagest_—_Tetrabiblos_ or _Quadripartitum_—A genuine reflection of Ptolemy’s approval of astrology—Validity of Astrology—Influence of the stars not inevitable—Astrology as natural science—Properties of the planets—Remaining contents of Book One—Book Two: regions—Nativities—Future influence of the _Tetrabiblos_. “_When the stars twinkle through the loops of time._” —_Byron._ [Sidenote: Seneca’s _Natural Questions_.] In this chapter we shall preface the main theme of Ptolemy and his sanction of astrology by a consideration of another and earlier ancient writer on natural science who was very favorable to divination of the future, namely, the famous philosopher, statesman, man of letters, and tutor of Nero, Lucius Annaeus Seneca. In point of time his _Natural Questions_, or _Problems of Nature_, is a work slightly antedating even the _Natural History_ of Pliny, but it is hardly of such importance in the history of science as the more voluminous works of the three great representatives of ancient science, Pliny, Galen, and Ptolemy. Nevertheless Seneca was well known and much cited in the middle ages as an ethical or moral philosopher, and the title, _Natural Questions_, was to be employed by one of the first medieval pioneers of natural science, Adelard of Bath. Seneca in any case is a name of which ancient science need not be ashamed. He tells us that in his youth he had already written a treatise on earthquakes;[475] and in the present treatise his aim is to inquire into the natural causes of phenomena; he wants to know why things are so. He is aware that his own age has only entered the vestibule of the knowledge of natural phenomena and forces, that it has but just begun to know five of the many stars, that “there will come a time when our descendants will wonder that we were ignorant of matters so evident.”[476] [Sidenote: Study of nature as an ethical substitute for existing religion.]