This structure was erected in 1883 and was used as a repeater-station for harbour signals between the observatory and Signal Hill. In 1895 its height was increased from 5.1m to 10.2m. Initially the ball was hand operated but its mechanism was electrified in 1903 and in 1934 the system was replaced altogether by radio signals. It was declared a National Monument under old NMC legislation on 27 August 1982.
The time ball is an obsolete time signalling device. It consists of a large, painted ball that is dropped at a predetermined time, principally to enable navigators to verify their marine chronometers from their ships offshore.
The first time-ball in Cape Town stood on a wooden tower mid-19th century in Observatory. With the development of the docks in the 1860's this ball was no longer visible to ships in the harbour. The second time-ball was built on the slopes of Signal Hill. This was replaced by this tower in the V&A Waterfront.
Built in 1894, the time ball in the Victoria & Alfred Waterfront remained in use for 40 years. In the period after that it was used as repeater station for harbour signals at some point. The tower was restored in November 1997.
The Cape Town ball is made of fibre glass. The dropping of the ball is triggered electronically by the SA Astronomical Observatory.
References
https://www.cape-town-heritage.co.za/heritage-site/time-ball-tower.html
Further Reading
https://www.sahistory.org.za/places/signal-hill