Notes Wieck (curator of medieval manuscripts at the Pierpont Morgan Library), ``The Book of Hours was the bestseller of the late middle ages.'' Heavily, often gorgeously, illustrated prayer books commissioned by the wealthy, they got their name because they contain a sequence of 37 prayers to the Mother of God intended to be recited throughout the course of the day. From the Morgan Library collections Wieck has drawn some 100 examples, reproduced in color. Much of the work is stunning, including a straightforward portrait of a meditative Christ, and a 1440 painting of a Bosch- like Mouth of Hell. The miniaturists who provided paintings for the books also decorated borders and even filled entire pages with abstract designs as well as with the tiny, precise figures of devils, angels, sinners, and saints. They also relied on their own world for inspiration for backgrounds, providing some wonderful views of medieval peasants and landscapes, castles and churches. Wieck provides a deft survey of the subject, and the illustrations, still fresh after six centuries, glowing with color and a fervent sense of faith, offer a unique glimpse of another time.