Spring diagram: Image courtesy of the Posner Memorial Collection, Carnegie Mellon University Libraries; London’s Memorial Tower: Matt Bridger / ​ DHD Multimedia Gallery; Royal Observatory: © National Maritime Museum, London
Diagrami i sustës: pamje me mirësjellje nga Posner Memorial Collection, Carnegie Mellon University Libraries; Kulla Përkujtimore e Londrës: Matt Bridger / ​ DHD Multimedia Gallery; Observatori Mbretëror: © National Maritime Museum, London