Plutarch’s Dialogue on _The Face in the Moon_ is not a scientific treatise, and its author would have disclaimed any intention of writing to advance science. It is discussion for the sake of discussion, the ‘good talk’ of which Plutarch wished that Athens should have no monopoly, any more than she had when the Boeotian Simmias and Cebes were among the trusted friends of Socrates, or, later, when ‘plain living and high thinking’ could be exhibited in lofty perfection in the Theban home of Epaminondas. A mixed company, which includes an astronomer, another mathematician, a literary man, and professed philosophers (there is no Epicurean here), with Lamprias, Plutarch’s brother, for president, discusses the movements and physical nature of the moon, from many points of view. Reference is made throughout to a previous discussion at which Lamprias, and Lucius, another of the speakers, had been present, when a person called ‘Our Comrade’ had dealt faithfully with the Peripatetic view, endorsed by the Stoics, that the moon is not of substance like our earth, but is a fiery or starlike body. This discussion had wandered into mystical theories as to the moon’s office in the birth and death of human souls, and her connexion with ‘daemons’. Sylla has joined the present company with a myth to relate bearing on these deep subjects, which had come to him at Carthage as a traveller’s tale. Its production is delayed until the end of the Dialogue, which it closes after the manner of a Platonic myth; the phrases with which it is opened and dismissed may be compared with those of the _Gorgias_. This double device, of referring part of the matter to a former conversation (as the _E at Delphi_ is a recollection of an old discourse by Ammonius), and part to a new and strange tale, skilfully relieves this elaborate Dialogue. Some difficulty is caused by the imperfect, or doubtful, condition of the text of the opening chapter, as no complete explanation seems to be given as to the place or time of the former discussion. Probably this abruptness is intentional, but the text requires careful attention. Perhaps this Dialogue throws more light on the views about the solar system accepted or under discussion in the first century of our era than a scientific treatise could have done. No reference is made to the great astronomical work of Ptolemy, which belongs to the second century, and closed most questions until the sixteenth. The estimate, e.g. of the moon’s distance (56 earth’s radii) is not Ptolemy’s (59). Some of the geographical details, as that of the Caspian Sea, seem to show that Ptolemy’s geographical work was not known to the Author. It may be useful to enumerate some of the simpler of the accepted views about the heavens : (1) That the earth is a Sphere was known to Pythagoras and allowed by Plato (_Phaedo_ 110 B), and affirmed by Aristotle, _De Caelo_, 2, 14, 297 b 18. The moon, and, according to Aristotle, the stars, are also spherical.