Astronomical Instruments and Their Users: Tycho Brahe to William Lassell (review)

In the third essay in this book, Allan Chapman identifies “the essential ingredients of a scientific problem” as “the need for accurate observation, exact instrumentation and conclusions based on careful measurements as opposed to purely theoretical criteria” (pp. 70–71). This point of view explains Chapman’s continuing interest in the relationship between the design and construction of astronomical instruments and the observations that could be and actually were made with those instruments. He brings to this task a familiarity with surviving instruments and a sophisticated reading of the documentary record, both astronomical and technological. Moreover, having replicated and then made observations with a number of historic instruments, he has a tangible appreciation of the skills needed to accomplish the various tasks involved.

The book contains several essays on the accuracy of scale graduations on various European instruments, a topic that Chapman discusses at length in his monograph Dividing the Circle: The Development of Critical Angular Measurement in Astronomy, 1500–1850 (New York: E. Harwood, 1990). The strength of this book, however, is the substantive essays on individual astronomers and instrument makers. One, for instance, concerns Tycho Brahe’s attention to and success with improving the stability and graduations of his angle-measuring instruments. Another pertains to the Tychonic instruments that the Jesuit missionary Ferdinand Verbiest built for the Imperial Observatory in Peking in the 1670s. This essay is largely based on Verbiest’s text and 105 woodcut illustrations showing the instruments and many construction techniques. Yet another describes Chapman’s reconstruction of two of Pierre Gassendi’s large angle-measuring instruments that Gassendi’s hometown commissioned for the four-hundredth anniversary of his birth in 1992.

Most of the essays in this collection pertain to English astronomy. The earliest concerns Jeremiah Horrocks, whom Chapman describes as “one of the first men in England to grasp the significance of what was going on in contemporary European astronomy” (p. 334). Chapman wrote the piece on the 350th anniversary of the 1639 transit of Venus, an astronomical event that Horrocks was the first to predict and observe. To understand Horrocks’s investigations better, Chapman replicated his technique for measuring the solar diameter and achieved similar results. One essay studies George Graham, the first important English artisan to apply scientific experiments and understanding to the design of instruments. Another examines Jesse Ramsden, whose linear and circular dividing engines mechanized the production of the graduated scales needed for practical purposes such as navigation, surveying, and architecture. Ramsden’s apparatus provided the funds that enabled him to make innovations in research apparatus for astronomy and geodesy.

Three essays in the collection pertain to English astronomers who expanded the light-gathering power of their telescopes and used these instruments for physical rather than positional work. In his account of William Herschel, written for the 250th anniversary of his birth, Chapman explains that Herschel saw the telescope not as an adjunct to the graduated scale but as his primary tool of investigation. An essay about William’s son, John Herschel, celebrates the two-hundredth anniversary of his birth in 1992. Chapman calls attention to his personal fortune, which paid for the apparatus and the leisure he used for his original research. (In one year at the Cape of Good Hope, Herschel spent more than seven times the annual salary of the Astronomer Royal at Greenwich.) After acknowledging the importance of the money that William Lassell earned from his brewery, Chapman turns his attention to the details of casting and polishing metal mirrors, and the mechanics of the large equatorial mounts that enabled astronomers to track astronomical objects as the earth turned on its axis.

Alas, the publisher of this volume is not as concerned with style as were the astronomers and instrument makers of whom Chapman writes. The seventeen essays collected here first appeared in various journals published between 1976 and 1994, and each retains its original pagination and style of footnotes or endnotes...