Western Astrolabes (review)

Western Astrolabes. By Roderick Webster and Marjorie Webster. Chicago: Adler Planetarium and Astronomy Museum, 1998. Pp. xiii+179; illustrations, bibliography, index. $45.

The astrolabe has become a symbol of medieval and Renaissance science. Yet few who see such striking instruments appreciate their function, complexity, variety, or history. Everyone who works in the field of medieval astronomical instrumentation has benefited by the generous and enthusiastic assistance of Roderick and Marjorie Webster, for many years curators of the collection at the Adler Planetarium in Chicago. Their catalog of western astrolabes has now been published, the first of a multivolume set that will be issued on the entire collection (under the general editorship of Bruce Chandler). Unfortunately, Rod Webster died before this first volume appeared.

The catalog opens with a history of the Adler Planetarium collection, begun in 1929 when Max Adler purchased the majority of instruments acquired by Anton Mensing of Amsterdam (the remainder, mostly globes, are now in the National Maritime Museum at Greenwich). Additional purchases were made between 1933 and 1958, with further enhancement of the collection through gifts from Kenneth Nebenzahl, David Pingree Wheatland, Stillman Drake, and the Websters themselves.

Sara Schechner Genuth contributes an opening essay on the cross-cultural and social perspective of the astrolabe, in which she summarizes evidence regarding its origins and diffusion as well as its uses and shortcomings. The astrolabe was a multipurpose device, a portable model of the heavens that was also an instrument for measuring altitude and an analog computer. Astrolabes could be fine examples of craftsmanship in brass--at times considered jewels to ornament a clock or a book binding--or they could be made of such mundane materials as wood covered with paper.

The catalog itself begins with a technical introduction to the astrolabe in general, with diagrams to assist in the explanation of various types. The vast majority of astrolabes preserved today are planispheric; only one spherical and a fragment of another are known to exist. Planispheric astrolabes can be divided into subclasses, depending upon the method of projection employed by the maker. By far the most common method was a south stereographic projection of the star map and other coordinates, which the Websters have termed "classic-type." Since astrolabes of this form required separate plates for different geographical latitudes, there were various attempts to design a "universal" astrolabe that could be used at any latitude. These projections are generally known by the name of their inventor, such as Azarquiel/Gemma Frisius (a projection devised independently in the eleventh and sixteenth centuries), de Rojas, le Hire, and Blagrave. Occasionally an astrolabe maker combined the standard stereographic projections with one of the other designs, in which case the Websters have classified the instrument as a "multiple-type."

Mariner's astrolabes (heavily weighted but with open areas to reduce wind resistance) were a postmedieval development. Also a late development was the surveyor's astrolabe, stripped of features considered superfluous to surveying, such as the open-work star map, the plates for different latitudes, and the astrological elements. Although a later volume will address surveyor's astrolabes in detail, this catalog includes one sixteenth-century surveying instrument made in Germany.

The collection represented here is probably the third largest in the world (after Oxford and Greenwich). The earliest western astrolabe is an English "classic-type" of about 1250. There are twenty additional classic-types, of which four are twentieth-century products. Three "multiple-type" astrolabes were made in Louvain in the sixteenth century. In the seventeenth century one German multiple-type and one English Blagrave-type were produced, and, in the eighteenth, three German and one French de Rojas-type. The one le Hire-type was made early in the twentieth century. The mariner's astrolabe is represented by a Portuguese piece made in 1616 and a copy made in 1963 of an astrolabe dated 1602, now in the National Museum of American History. The volume also includes astrolabe-quadrants, with ten examples dating from the period 1550-72. A particularly...