Ever wondered what's the source of the famous pip-pip-pips sound heard on BBC radio marking the hour.
This astronomical regulator was originally made for use in observing the Transit of Venus in 1874.
In 1923 it was adapted as the primary standard for the new six-pip time signal. The clock sent electrical impulses down a telephone wire to the BBC for conversion into audio pips for radio broadcasts.
This clock was in service for the BBC signal at the Observatory from 1924 to 1949, when it was superseded by a quartz clock.
The three sets of contacts for closing the six-pip circuit every quarter of an hour can be seen in two of the holes within the seconds dial, and halfway down the pendulum, operated by a roller.