Sky & Telescope January 1981 [antikvár]

ASTRONOMICAL SCRAPBOOKEarly Textbooks with Moving PartsN' OWADAYS. every basic textbook seems to require a selection of color plates to compete in the astronomical marketplace. In the 16th century the equivalent enticement was a set of diagrams with movable parts, and. in fact, the great majority of textbooks contained precisely the same three devices.Relatively inexpensive astronomy texts were a rather newfangled idea in the 1530's. Although printing with movable type had not yet celebrated its centenary, presses had swept throughout Europe with astonishing speed, bringing higher rates of literacy and far easier access to textual material. The first astronomical printer, Regiomontanus, had opened a printing shop in Nuremberg around 1470, and one of his first books included a diagram with two rotating disks for determining the motion of the moon. But none of his editions, nor any of the astronomy books of the 15th century, could be properly considered an astronomy text.Not until the 1530's. at the University of Wittenberg, did astronomy books appear in the small "octavo" format that was cheap enough for students to be expected to buy their own copies. Like almost all books of that century, they were sold as paperbacks; the binding, if any. was left to the discretion of the owner. For the next several decades the presses at Wittenberg turned out new but scarcely revised editions every few years.Like modern textbooks, those of 16th-century Germany became obsolete or worn out. so that today any particular edition can be quite rare, especially with the moving parts complete. Consequently. I have been able to make only spot checksThe first set of volvelles, unassembled, from an edition of Sacrobosco's Sphaera printed in Venice in 1620. The upper right circle provides the base for the moving parts below. For assembly instructions, see the caption to the third set on page 6. The volvelles in this article are all reproduced at nearly the same scale as the originals.with respect to these early editions. But in doing so, I gradually realized that virtually all of them contain diagrams with moving parts, called volvelles. and virtually all have three almost identical setups.The first standard diagram with moving parts, or "volvelles," in an edition of Sacrobosco's Sphaera printed at Antwerp in 1573. The diagram illustrates how an eclipse is seen differently with respect to the horizon for observers in different longitudes, showing that the earth is round in an east-west sense.Before describing these three devices, and showing you how to make your own set. I must mention that the standard introductory textbook went back to John of Holywood, a 13th-century English mathematician and astronomer who was educated at Oxford but who spent most of his adult life in Paris. There he was known by his Latinized name. Johannes de Sacrobosco.Sacrobosco's Sphaera was divided into four chapters. The first dealt with the shape and immovable place of the earth within the spherical universe and. in the printed textbook editions, contained the first two volvelles. Chapter 2 treated the various circles of the earth and sky, while Chapter 3 described risings and settings from various geographical locations, and in the printed textbooks contains the third volvelle. The fourth and least satisfactory chapter gave a very brief description of Ptolemy's planetary theory and of eclipses; it was so scanty that students of the 16th century who wished to pursue astronomy further turned to a more advanced text, generally Georg Peurbach's Theoricae novae planetanim. Like the Sacrobosco, the Peurbach text was printed in numer-4 Sky and Telescope, January, 1981