Its history is rather hazy, except for the fact that in 

 1 780 this second Borghesi timepiece was still in the 

 Imperial Palace in Vienna. The clock was again 

 noted in 1927 when it was sold at a public auction in 

 New York. 2 Subsequently, it was acquired for the 

 Smithsonian Institution. 



Development of Astronomical Clocks 



The history of the great theoretical and mechanical 

 achievement which the Borghesi clock represents has 

 been most adequately covered elsewhere. 3 Considera- 

 tion of the development of equation and astronomical 

 clocks is required here only for the purpose of relating 

 the Borghesi timepiece with the other significant 

 developments in this branch of horology. 



The invention of the anchor escapement in about 

 1670, and the consequent greater accuracy in time- 

 telling, led to increased preoccupation with precision. 

 Daily differences in time as recorded by sundials and 

 clocks became more noticeable. Finally, in the second 

 half of the 1 7th century, some attempt was made to 

 construct mechanical clocks combined with sundials 

 as well as astronomical clocks. 



With the improvement of precision time-telling, it 

 became necessary to reconcile the actual difference 

 between true and mean time. Although a great variety 

 of time-equation tables were produced, there was a 



2 Wenham, "Tall Case Clocks," p. 33. 



3 Von Bertele, "The Development of Equation Clocks," 

 parts 1 through 5. 



considerable margin for error in their use. This led 

 to the construction of mechanical clocks in which the 

 equation of time was automatically accomplished. A 

 few were produced late in the 17th and early 18th 

 century at considerable cost and, consequently, with 

 little popularity. Equation sundials were also devel- 

 oped which were elaborately ingenious, but they were 

 not completely practical. Inevitably, they were sup- 

 planted by the mechanical equation clock. 



Probably the first documented mention of an equa- 

 tion clock is in the diary of John Evelyn who recorded 

 that in 1666 he visited the Royal Society where he 

 witnessed a curious clock, which showed the equation 

 of time, being presented by a certain Mercator. More 

 data on the subject appeared in the first two decades 

 of the 18th century, when Henry Sully, Joseph Wil- 

 liamson, Daniel Quare, and Thomas Tompion — who 

 were among the foremost English clockmakers of all 

 time — produced elaborate examples of these time- 

 pieces. Another significant maker was Dowe Wil- 

 liamson, who became Court Clockmaker to Emperor 

 Charles VI of Austria. In London, Joseph William- 

 son produced some of the finest astronomical time- 

 pieces of this type that have been known. The interest 

 in the subject next shifted to France where many fine 

 examples were produced during the first half of the 

 18th century. 



Just after the middle of the 18th century, the subject 

 of astronomical clocks suddenly became a major 

 horological preoccupation in another region, namely, 

 Austria, where the work in this field was apparently 

 done exclusively by members of the clergy. The 



ACKNOWLEDGMENTS 



The author wishes to acknowledge the valuable 

 assistance received from the following: Dr. Amos 

 Avery, Amherst, Massachusetts; Mr. Edwin A. 

 Battison, curator of light machinery and horology, 

 U.S. National Museum; Dott. Richard Blaas, 

 Oesterreiches Staatsarchiv, Vienna; Dott. Adolfo 

 Cetto, librarian, Biblioteca Comunale di Trento, 

 who made copies of Borghesi's two volumes available; 

 Signor Mario di Mario, editor of La Clessidra, 

 Rome, who permitted several of the illustrations in 

 Sig. Luigi Pippa's article to be used herein; Mr. 

 Walter A. Gilbert, Norwich, Connecticut; Dr. 

 Heinrich Linardi, Uhrenmuseum der Stadt Wien, 

 Vienna; Signor Luigi Pippa, Milan, Italy; Cav. 



Ing. Guido Ucelli di Nemi, Presidente, and Dott. 

 Federico Morelli and Cav. Orazio Curti of the 

 Museo Nazionale della Scienza e della Tecnica, 

 Milan, for their cooperation on the descriptions and 

 illustrations of the restored clockshop of Bartolomeo 

 Antonio Bertolla; and Dr. Edward Waters, Division 

 of Music, Library of Congress, Washington, D.C. 

 The translation from Francesco Borghesi's Latin 

 texts, which made this study possible, were made by: 

 Rev. Neil Herlihy, S.J., Rev. Francis J. Heyden, 

 S.J., and Rev. Stephen X. Winters, S.J., George- 

 town University, Washington, D.C; and Rev. 

 Daniel Hunter, O.P., and Rev. Robert Stenger, 

 O.P., Dominican House of Studies, Washington, D.C. 



32 



BULLETIN 240: CONTRIBUTIONS FROM THE MUSEUM OF HISTORY AND TECHNOLOGY 



