Karl Friedrich Zollner and the historical dimension of astronomical photometry

This book results from presentations and discussions of a group of astronomers and historians during a one-day workshop held at Archenhold Observatory, Berlin-Treptow, on April 4, 1997. This meeting was the first forum in a series dedicated to historical aspects of observational astrophysics in the nineteenth and early twentieth century. The basic principle of these meetings is to reflect during one or more days on the work and personality of a single individual or of a group of persons, at the same time avoiding the really dominant figures that typify the age. By focusing on key people who epitomize a way of thinking and working that has formed many of the ideas by which we do astrophysical research today, we also attempt to evoke the scientific spirit of the era under consideration. In 1858, the German physicist Karl Friedrich Zoellner introduced a new type of astronomical photometer which became a bestseller in the second half of the nineteenth century and which led him to the first German professorship in astrophysics. His type of photometer allowed most accurate photometric measurements and was used at several observatories for almost half a century. This book outlines four major themes. The first part describes the observing instruments that were used by Zoellner and his contemporaries: photometers and spectrographs that complemented his original design, but also competed with his most versatile prototype photometer. The description also includes an account of technical aspects associated with the replication of such a photometer today. The second part analyses the astrophysical data that were obtained with Zoellner's tools, and extracts information hidden in the published data --- scientific information as well as diverse aspects related to the observer himself. These nineteenth-century data are now published for the first time on a modern magnitude scale and are directly accessible in tabular form, and are thus fully applicable to archeophotometric studies. The third part of the book illustrates some aspects of Zoellner's personal life, his correspondence, and the relationship to his direct colleagues. It follows Zoellner during the last years of his life when he experienced severely strained relationships with the scientific establishment of his time. The last part reviews a number of scientific studies made on the most enigmatic personality that Zoellner certainly was, and also gives a bibliography of all works by Karl Friedrich Zoellner which were published during his lifetime or which appeared posthumously.