An eight-day astronomical alarm designed by Thomas Taylor and made by Grimalde & Johnson circa 1827

The single fusee movement has rectangular plates, which are signed by the manufacturer, half dead-beat escapement and alarm train which is wound by pulling a cord. The 24 hour silvered dial is rotated by the movement (rated to show sidereal time) and carries pins that provide an hourly passing strike. The dial also features a concentric ring of holes, any one of which when filled by a brass peg will activate the alarm at the appropriate time. There are 144 holes on the dial which allow for a maximum of an alarm every ten minutes. The clock is fitted with an alarm silence and after each ring the observer would have to re-wind the alarm train by pulling the cord.

Thomas Taylor was First Assistant at the Royal Observatory from 1807 to 1835 and it was during this time that he devised the clock. The holes in the dial correspond with the transits of ‘clock stars’, which were observed whenever the weather permitted. Unlike a standard alarm clock, Taylor’s design could be pre-set to alert the resting observer that a transit was imminent. Taylor was awarded 15 guineas for his invention by the Society of Arts in 1819.