Of the astral influence which was considered to have originated the “_Great Mortality_,” physicians and learned men were as completely convinced as of the fact of its reality. A grand conjunction of the three superior planets, Saturn, Jupiter and Mars, in the sign of Aquarius, which took place, according to Guy de Chauliac, on the 24th of March, 1345, was generally received as its principal cause. In fixing the day, this physician, who was deeply versed in astrology, did not agree with others; whereupon there arose various disputations, of weight in that age, but of none in ours; people, however, agreed in this—that conjunctions of the planets infallibly prognosticated great events; great revolutions of kingdoms, new prophets, destructive plagues, and other occurrences which bring distress and horror on mankind. No medical author of the 14th and 15th centuries omits an opportunity of representing them as among the general prognostics of great plagues; nor can we, for our parts, regard the astrology of the middle ages, as a mere offspring of superstition. It has not only, in common with all ideas which inspire and guide mankind, a high historical importance, entirely independent of its error or truth—for the influence of both is equally powerful—but there are also contained in it, as in alchymy, grand thoughts of antiquity, of which modern natural philosophy is so little ashamed that she claims them as her property. Foremost among these, is the idea of the general life which diffuses itself throughout the whole universe, expressed by the greatest Greek sages, and transmitted to the middle ages, through the new Platonic natural philosophy. To this impression of an universal organism, the assumption of a reciprocal influence of terrestrial bodies could not be foreign[170], nor did this cease to correspond with a higher view of nature, until astrologers overstepped the limits of human knowledge with frivolous and mystical calculations.