This rare work by the mathematician Jean Oursel is a mixture of astronomy and astrology. As well as providing information upon the calculation of the phases of the moon – with the use of a volvelle – and the measuring of time by the use of a sundial; the work also covers the effect of the moon’s phases upon a person’s health; and provides a perpetual calendar for the calculation of religious feast days.

Little is known of mathematician and publisher Jean Oursel, although a brief view of the other works published around the time give a sense of his interests: in 1678 published two works one upon the cures for numerous illnesses, and the other an introduction to astrology; and in the same year as he published a book on the prophecies of Nostrodamus. One should also not confuse him with his son Jean Oursel (1672-1727), who was also a publisher and poet working in Rouen.