Observation, working images and procedure: The Great Spiral in Lord Rosse's astronomical record books and beyond

Abstract

This paper examines the interrelations between astronomical images of nebulae and their observation. In particular, using the case of the Great Spiral (M51), we follow this nebula beginning with its discovery and first sketch made by the third Earl of Rosse in 1845, to giving an account, using archival sources, of exactly how other images of the same object were produced over the years and stabilized within the record books of the Rosse project. It will be found that a particular procedure was employed using working images that interacted with descriptions, other images and the telescopic object itself. This stabilized not only some set of standard images of the object, but also a very potent conception of spirality as well, i.e. as a normal form. Finally, two cases will be contrasted, one being George Bond's application of this spiral conception to the nebula in Orion, and the other Wilhelm Tempel's rejection of the spiral form in M51. Copyright © 2010 British Society for the History of Science.