Congreve's rolling ball clock, presented in 1808 to the Prince Regent, the future King George IV. Collection of the Royal Artillery Historical Trust. On loan to a semi-permanent exhibition dedicated to the Royal Artillery and Royal Military Academy in Greenwich Heritage Centre, Woolwich, south east London, UK.
<a href="//commons.wikimedia.org/wiki/User:Kleon3" title="User:Kleon3">Kleon3</a>
<span class="int-own-work" lang="en">Own work</span>