In a span of a week in September, 2023 an earthquake ravaged Morocco, a green comet appeared in the sky, and a cyclone caused extensive floods in Greece and Libya. In antiquity, these events would be studied under the heading of μετεωρολογία and were the sort of phenomena that philosophers from Anaximander to Aristotle to Seneca investigated. Posidonius, a Stoic philosopher active primarily in the first century BCE, wrote extensively about meteorological matters, but only fragments remain of his voluminous works. Hall’s monograph aims to give a holistic view of Posidonius’ meteorological writings and of their importance for later writers and thinkers. It succeeds in doing so and sheds important light upon Posidonius’ ideas, but with some caveats, detailed below.
The book is formatted into short chapters. The opening chapters lay out the background (e.g. “The biography and later reputation of Posidonius”) and act to define the term “meteorology” and even the region in which meteorological phenomena arise. For someone with a basic knowledge of philosophy or the meteorological tradition, these chapters are rather rudimentary. There are some gems, however, such as Hall’s assertion that Posidonius was an innovator of Stoic ideas about meteorology (30) and the manner in which Posidonius had to grapple with Aristotle’s concept of the heavens (with its fifth element) in his own meteorological theories (37). Often, however, it feels that Hall is simply reporting textbook knowledge without connecting the dots or making an argument about Posidonius’ meteorology. For instance, a deep dive into astronomical calculations of the sun’s relative size and distance from the earth leads only to the indecisive “But Posidonius’ relative success was the result of chance—unless one likes to call it intuition” (44), without any discussion of what the consequences of such calculations had on Posidonius’ meteorological views. The book as a whole lacks an overarching argument, and the chapters often stand alone and conclude with variations of a non liquet summation. Throughout these chapters, however, Hall is careful to cite the primary sources and his detailed notes will be a boon for scholars.
The central section of the work discusses the phenomena themselves, with chapters on topics such as “lights in the sky”, “earthquakes and volcanoes”, and “weather prediction and divination”. These are succinct overviews of the topics that feature earlier opinions before giving Posidonius’ interpretation. Aristotle often looms large as a source and Posidonius usually treats his views, and those of earlier Stoics, with respect. For example, Hall’s discussion of comets moves from Xenophanes’ idea that they were the movement of burning clouds through other pre-Socratic thinkers before dwelling on Aristotle’s view and those of the Stoics prior to Posidonius. Hall points out how Posidonius’ idea resembles Aristotle’s because of its reliance on exhalations and how Posidonius’ own theory held sway for certain later thinkers such as Arrian. The chapter on winds is particularly informative and holistic with sections on characteristics of local winds, on the wind-rose, and (speculatively) on why ancient thinkers debated the causes of winds, as well as on Posidonius’ own ideas about winds. Likewise, his chapters on the sea and its tides and on the flooding of the Nile are rich in detail and show how Posidonius’ wide interests in eye-witness reports, geography, and travel, as well as his own open mind to various thinkers, helped him to make discoveries that were original, and, in the case of the Nile’s flood, true. Posidonius urged Stoics to move beyond sense perception and utilize reason as a criterion of truth, and Hall’s chapter on Posidonius’ “Sources and Methods” does a nice job pointing out how syllogisms and axiomatic thinking underlie many of Posidonius’ meteorological theories.
My primary caveat is that because many chapters do not engage with Posidonius’ ideas in a very critical manner, the majority of the book reads like long encyclopedia entries. While Hall is always sure to contextualize Posidonius’ theories within the broader philosophical tradition, it is rare for him to zoom out and give further information about how this aspect of Posidonius’ Stoicism might impact his larger Stoic views. The final chapters address some of the wider issues—including, for instance, a comparison with Epicurean meteorology—and offer an assessment of Posidonius and his successors as a conclusion. After reading the book, however, one still feels that Kidd’s pronouncement holds true:
It is infuriating that because of our fractured evidence, and more particularly because of the limited interest and understanding of men like Strabo, who used his more scientific works, but disapproved of his deeper aetiological interests, that [sic] we are now lacking demonstration of how Posidonius actually operated on the borderline where for him philosophy and science met, in the limbo-land of hypotheses and the differentiation between different kinds of causes and explanations.
Hall has authored a basic doxography, much like works such as Seneca’s Naturales Quaestiones (which often engages with Posidonius), but without the juicy digressions or sublime aspirations of Seneca’s work. This sober and judicious work surveys the major fragments and evidence of Posidonius’ meteorology and can orient the reader vis-à-vis the doxographical tradition of meteorology, but the whole is not greater than the sum of its parts.
 See L. Edelstein and I. G. Kidd’s magisterial three-volume edition (Cambridge: Cambridge University Press, 1989-1999).
 E.g., on lights in the sky: “But, if Posidonius did believe that unusual celestial events were portents, we have no details of his views” (76); on rainbows: “He probably supported his rainbow theory with geometrical arguments, but we have no idea what they were. I have suggested that he is likely to have been interested in the phenomenon of refraction, but definitive evidence is lacking” (168).
 “[A] comet is formed when some dense air becomes fixed in the revolving aithēr which form the heavens, and this dense air catches fire and is carried round with the aithēr, sustained by a continuous flow of vapour from below” (80-1).
 Which can be seen, broadly speaking, in Seneca’s meteorological work, Naturales Quaestiones, as Gareth Williams clarifies: “Seneca’s approach to the natural world begins within the viewer, preconditioning the self to a vision of natura ipsa that is unimpeded by blinkered, everyday ways of seeing” (The Cosmic Viewpoint: A Study of Seneca’s Natural Questions. Oxford: Oxford University Press, 2012, 29).
 In my opinion, Hall underestimates the interest and importance of the study of physics and meteorology for the Epicureans. See L. Taub’s chapter “Cosmology and meteorology” in J. Warren, ed., The Cambridge Companion to Epicureanism. Cambridge: Cambridge University Press, 2009, 105-24.
 I. G. Kidd, Posidonius III. The Translation of the Fragments. Cambridge: Cambridge University Press, 1999, 8.