humanity is the sport of these infirmities. When man’s conception of Divine Providence had sunk so low, it was well that Imperial Rome should be without religion. Manilius, in his _Astronomica_,[94] composed about the Christian era, asserts with confidence, that comets presage pestilence. The belief is probably far older than Manilius, though it is difficult to cite exact authorities. Livy[95] speaks of a bright light in the sky before the plague of 462 B.C.; ‘coelum ardere visum est plurimo igni’: and Dionysius of Halicarnassus[96] recounts the lighting up of a fire in the heavens before that of 450 B.C.: ἐν οὐρανῷ σέλα φερόμενα καὶ πυρὸς ἀνάψεις. Allusions such as these would seem to signify the appearance of a comet. Vergil[97] is even more explicit: Non secus ac liquida si quando nocte cometae Sanguinei lugubre rubent, aut Sirius ardor, Ille sitim morbosque ferens mortalibus aegris Nascitur, et laevo contristat lumine coelum. Of their supposed malign influence on human affairs in general there is no doubt. Tacitus[98] assigns to them even a political significance, for he says that in popular opinion they always portend a revolution to kingdoms. Seneca,[99] in his _Physical Science_, makes the specific statement that ‘after great earthquakes it is usual for a pestilence to occur’. The concurrence of the two had been mentioned previously by Thucydides, Diodorus Siculus, Livy, and others, but Seneca would seem to be the first to attempt to define the exact relation of the one to the other. In the Campanian earthquake of A.D. 63 a flock of 600 sheep had perished mysteriously, near Pompeii. Seneca conceives that earthquakes liberate poisonous fumes imprisoned in the earth, or pent up in marshes, which serve to taint the air. Flocks suffer most, he thinks, because they live in the open, and also drink the poison-laden water. They feed too with heads close to the ground and so receive the concentrated venom, before it has become diluted: and then he adds: ‘If it had issued in greater volume, it would have injured man too, but the abundant supply of pure air counteracted it, before it could rise high enough to be breathed by any human being.’ And he proceeds: ‘The better is ever conquered by the worse. Even that pure air of heaven changes then to pestilential. Thence come sudden and continuous deaths, and portentous forms of disease, that spring from unexampled causes. The disaster is long-or short-lived according to the strength of the sources of infection. Nor does the plague cease, until the freedom of heaven and the tossing of the winds have banished that fatal air.’