Today few would think of astronomy and astrology as fields related to theology. Fewer still would know that physically absorbing planetary rays was once considered to have medical and psychological effects. But this was the understanding of light radiation held by certain natural philosophers of early modern Europe, and that, argues Mary Quinlan-McGrath, was why educated people of the Renaissance commissioned artworks centered on astrological themes and practices. Influences is the first book to reveal how important Renaissance artworks were designed to be not only beautiful but also-perhaps even primarily-functional. From the fresco cycles at Caprarola, to the Vatican's Sala dei Pontefici, to the Villa Farnesina, these great works were commissioned to selectively capture and then transmit celestial radiation, influencing the bodies and minds of their audiences. Quinlan-McGrath examines the sophisticated logic behind these theories and practices and, along the way, sheds light on early creation theory; the relationship between astrology and natural theology; and the protochemistry, physics, and mathematics of rays. An original and intellectually stimulating study, Influences adds a new dimension to the understanding of aesthetics among Renaissance patrons and a new meaning to the seductive powers of art.