Message #27002

[Bianca]

                             

                                                          The back dials

The upper back dial displays a four year period and has five concentric inscribed rings, most probably each with 47 divisions giving the Metonic Cycle of 235 synodic months, which equals 19 solar years. The lower back dial gives the cycle of a single synodic month, and the subsidiary dial the Lunar year of 12 synodic months.

The original gearing was cut from bronze, and the 60 degree triangular teeth were finished using a file. In the reconstruction, the gearing is made from brass, set between perspex plates, with perspex dials in place of the original bronze, so that the mechanism is visible.

The instrument indicates that the technology of the time, of which this is the only surviving example, was by any measure sophisticated.

John Gleave can be reached at:-
Tel & Fax 01422 844837