Clock Tower on Exhibit in NMHT, by Unknown, 1970s, Smithsonian Archives - History Div, A reconstruction of a Renaissance clock tower in the Hall of Light Machinery, Museum of History and Technology (MHT), now the National Museum of American History (NMAH). The basic clock mechanism is that of the town clock of Frederick, Maryland, made by clockmaker Frederick Heisley in 1790. On each face of the clock tower is a different kind of dial: a sundial (shown on the right), a civil time dial (here being installed by John Vernon of Thwaites & Reed, London), an astronomical dial and an automaton dial. Each was specially designed for this exhibit..