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
איור של קפיץ: Image courtesy of the Posner Memorial Collection, Carnegie Mellon University Libraries; אנדרטת הזיכרון בלונדון: Royal Observatory: © National Maritime Museum, London; Matt Bridger / DHD Multimedia Gallery