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Book Review: Astronomical Spectrographs: Astronomical Spectrographs and Their History

and other astronomical instruments of the Middle Ages. Finally, the restorer Lothar Hasselmeyer and the late curator Joachim Schardin examined the clock’s history and design. It should be noted that most of the work was executed under difficult circumstances; until 1990 Germany was a divided country and personal contacts were by no means easy. Scant financial resources following German unification made a publication of the results rather implausible. The market for such specialized and demanding books is a very narrow one, and consequently no profit whatsoever can be expected. Therefore it is highly commendable that due to support of the Deutsche Gesellschaft für Chronometrie in Nuremberg this work has been made accessible by their releasing it in the series of that society’s yearbooks. During most of the late medieval period, either tables or equatoria were used to calculate planetary positions. Astronomical clocks indicating planetary positions could be designed with concentric dials (e.g., the astronomical clock by Philipp Imsser and Gerhard Emmoser in the Technical Museum in Vienna), or by using a set of equatoria driven by clockwork. The prototype of the latter design was the “Astrarium” built by Giovanni de Dondi in the fourteenth century; in addition to the Dresden clock there is another famous example made by Baldewein in the Astronomical-Physical Cabinet in Kassel and the astronomical clock now preserved in the Bibliothèque Sainte-Geneviève in Paris. Such highly complicated clocks, which served astrological purposes, functioned as analogue computers to indicate time, planetary longitudes and latitudes, and calendrical data. Ptolemy’s planetary theory is visualized mechanically. This book thus opens with a concise exposition of Ptolemaic astronomy (pp. 21–35). Two chapters on the history of the Dresden clock (pp. 37–43) and its design (pp. 45–63) follow. The core of the book provides a painstaking documentation of the mechanisms, dials and indications (pp. 65–242). An appendix lists parameters and a glossary of astronomical terms (pp. 243–53). The book is illustrated sumptuously by numerous colour illustrations of high quality and several schematic diagrams. One would wish for similarly comprehensive studies of other important clocks and instruments.