Circles, Clocks, Ships, and Wires: Meridian Circles within Innovative Assemblages in 19th-Century America

Abstract

Driven by needs to map an expanding nation as well as by pure astronomical inquiry, nearly 50 meridian circles were installed in 19th-century U.S. observatories. In the 1840s, U.S. astronomers used meridian circles in conjunction with chronometers on fast steamships to ascertain transatlantic longitude differences. Simultaneously, they devised methods of using meridian circles with newly invented telegraph technologies, which revolutionized longitude determination, productivity of data collection within observatories, and distribution of time signals. 19th-century U.S. astronomers and artisans also designed improvements to meridian circles themselves; by century end, U.S.-based instrument makers dominated the domestic meridian circle market over English and German artisans.