This book is one of the most famous post-classical astrological works. The author William Lilly obviously has very good instincts. His famous prediction of the Great Fire of London in 1666 was so accurate that some people suspected that he was his initiator, and he was later found not guilty. Lilly also uses astrology in medical practice. This book discusses the use of astrology in diagnosing diseases and determining whether patients will die or get better. This book was first published in 1647 as Christian astrology.

William Lilly (1602 1681) was a seventeenth century English astrologer. He is described as having been a genius at something "that modern mainstream opinion has since decided cannot be done at all" having developed his stature as the most important astrologer in England through his social and political connections as well as going on to have an indelible impact on the future course of Western astrological tradition.