Abstract
Judging by the title, we are dealing with an account of astronomical observations, of star positions in particular, completed over three days and three nights in October 1706. These observations did not result in any major breakthroughs in the history of astronomy, so why should we read 800 pages in three volumes about them? These initial doubts are entirely alleviated while reading Ole Rømer’s Triduum. The book offers far more than its title promises, with regard to both historical and astronomical content, and represents a superb editorial project.
Ole Rømer (1644–1710) earned his place in the history of science due to his discovery of the finite velocity of light. This discovery resulted from the period of several years which he spent at the Paris Observatory. In 1681 Rømer returned to Denmark and in 1685 he became the director of the Copenhagen Observatory. In 1704 he built a small private observatory outside Copenhagen, the Observatorium Tusculanum, equipped according to his own innovative ideas. In both the Copenhagen and Tusculan observatories Rømer accumulated a vast store of astronomical observations. Almost all of them, together with Rømer’s meridian circle, perished in the 1728 Copenhagen fire. The manuscript of Triduum Römeri 1706 was more lucky as it did not share the fate of other Rømer’s observations, but also went through two editions in 1735 and in 1741, and now a third which is being presently reviewed.
Rømer’s Triduum would attract the attention of the successive generations of astronomers when the methods for reduction of observations were developed, taking into account individual sources of error, including instrumental errors. Rømer was ahead of his time in this respect and the Triduum observations were first to expose the great potential of meridian circles in positional astronomy, although it would take several dozen years before the next meridian circles were constructed. The key role in making Triduum observations available, as well as introducing Rømer’s instruments and ideas, was played by Peder Horrebow (1679–1764), a pupil of Rømer’s, in 1714 appointed professor of astronomy and director of the Copenhagen Observatory. Horrebow spent most of his scientific career in the continuation and preservation of Rømer’s work. The result of these efforts was the publication in 1735 his Basis Astronomiae sive Astronomiae pars mechanica, and in the years 1740–1741 the three volumes of Opera Mathematico-Physica, as well as Audytum Astronomiae left in manuscript.
The Triduum observations of stars and planets were treated by Rømer himself, even though his method is known only from the reconstruction done by Horrebow. Furthermore, Horrebow attempted the reduction of the Triduum observations in his Audytum, but his results were never published. In the years 1756–1760 Tobias Mayer (1723–1762) in Göttingen also sought to decompose the instrumental errors of Rømer’s observations. He established a mathematical expression for the correction to be added to the observed transit times due to the instrumental errors, today known as Mayer’s formula. However, as proven by the authors of the publication under review, this formula was already known to Rømer and Horrebow, but not published. An extensive analysis of the Triduum observations was conducted by Johann Gotfried Galle (1812–1910) in his doctoral dissertation as of 1845. A modern reduction of the Triduum observations is included in the work under review. I recommend this fragment to anybody wishing to know how to perform such calculations; the problem is presented in a manner which is reader-friendly and complies with relevant standards.
This edition includes three volumes. The first, “An introduction to the observations and a modern analysis,” focuses on the Triduum observations and presents the data of both Rømer and Horrebow, as well as a description of the Tusculan Observatory. Volume I has also 11 appendices: extracts of Rømer’s correspondence with Gottfried Wilhelm Leibniz devoted to the Tusculan Observatory and Rømer’s ideas for a meridian circle; Rømer’s discussion of the reduction of the right ascensions; Rømer’s recommendation of Horrebow for a degree in theology; an inventory of the instruments and machines remaining at the time of Rømer’s death; a short description of the meridian instrument from De instrumentis astronomicis (1713) by Joachim Frederik Rasmus, one of Rømer’s students; a letter from Horrebow to Johannes Lulofs from 1741 explaining some details about the Tusculan Observatory; an anonymous report on a visit to the Tusculan Observatory in c.1765; a laudatory poem to Horrebow by Niels Krogh (1721); extracts from Horrebow’s unpublished Adytum Astronomiae translated into English; detailed reduction of the Triduum observations; and a selection of five copperplates from Basis Astronomiae. Volume II reprints Horrebow’s Basis Astronomiae together with an English translation and some historical background. Volume III reproduces the Triduum manuscript, preserved in Royal Danish Library, together with a transcription and translation of the Latin notes. All three volumes are richly illustrated; the illustrations are reproduced according to the highest printing standards.
This interesting and beautiful book suffers from one deficiency; it lacks indices which would surely make life easier not only for the reviewer.
