At the ends of the line: How the Airy Transit Circle was gradually overshadowed by the Greenwich Prime Meridian.

The Greenwich Prime Meridian is one of the iconic features of the Royal Museums Greenwich. Visitors to the Museum even queue up to pose with one leg on either side of the Line. Yet, the Airy Transit Circle, the instrument that defined the meridian, is almost always excluded from these photographs. This paper examines how the instrument has become hidden in plain sight within the stories of Greenwich Time and Greenwich Meridian, as well as within the public imagination, by providing an analysis of the instrument's transformation from a working astronomical instrument to a museum object. The paper highlights the gradual decoupling of the instrument from narratives of Time and Longitude, which resulted in the Line's popularity overshadowing the instrument that defined it. By doing so, the paper aims at showing the symbiotic relationship between the materiality of the instrument and the meridian line that it defined. Approaching the instrument through the lenses of object biographies, the paper raises the question of whether the life of the instrument came to an end once operations with it were terminated. The analysis of the Transit Circle's life reveals that it reached its end multiple times, which shifts the emphasis away from a single and ultimate end of scientific objects to a process of gradual downfall, during which they can "end" several times. In addition, through the object biography approach, the Transit Circle no longer appears as a dead object reaching an afterlife within a museum setting. Instead, the approach demonstrates that, though the instrument can still be restored to an operational order, doubts about its accuracy, and its relevancy to today's astronomical methods, have led the instrument to be considered obsolete, transforming it into a museum object on display.