One O’Clock Gun

 History of Astronomy  No Responses »
Jun 222019
 

Castlehill, Edinburgh, EH1 2NG

The One O'Clock Gun positioned in the Half Moon Battery within the walls of Edinburgh Castle

One O’Clock Gun (© Roger Cornfoot via Wikimedia Commons)

Because of the poor Scottish weather, the notorious haar (sea fog), and smog, the time ball at the top of Nelson Monument on Calton Hill was rarely visible to the ship navigators in the ports along Leith and Newhaven who needed to accurately adjust their clocks. As such, in 1861, an 18-pound muzzle-loading cannon from the Half Moon Battery at Edinburgh Castle was commissioned into “Time Gun” service. Its present-day successor is still fired every day at precisely 1 o’clock, except for Sundays, Good Friday and Christmas Day. However, as the speed of sound is 343 metres per second (770 mph) and docks were about 2 miles (3km) away, the navigators had to account for about 10.5s delay when they set their clocks. This can be seen on the “Edinburgh Time Map” prepared by the 1 o’clock gun’s proposer, Charles Piazzi Smyth. Interestingly, the gun has also seen an instance of military action, as it was fired on 2 April 1916 at a German Zeppelin conducting an air raid during WWI.

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Black and white illustration of the Half Moon Battery within Edinburgh Castle

Half Moon Battery and firing mechanism in 1861 (Wikimedia Commons)

The time signal delay map designed by Piazzi Smyth

Time signal delay map designed by Piazzi Smyth (© Alastair Bruce)

Photograph of Edinburgh Castle showing the smoke after the One O'Clock Gun was fired

Smoke from the One O’Clock Gun (© Kim Traynor via Wikimedia Commons)

Time Ball on Nelson Monument

 History of Astronomy  No Responses »
Jun 222019
 

32 Calton Hill, Edinburgh, EH7 5AA

The Time Ball at the top of the Nelson Monument

Time Ball on Nelson Monument (© Kim Traynor via Wikimedia Commons)

In 1853, the second Astronomer Royal for Scotland, Charles Piazzi Smyth, secured the installation of a time ball at the top of Nelson Monument. This tower, which looks like an “upturned telescope” and is clearly visible from most of Edinburgh, was designed by the architect Robert Burn and erected in 1815. While an interesting curiosity these days, the time ball used to be vitally important to ships in the port of Leith in adjusting their clocks for navigation, as it was  raised and dropped exactly at 1 o’clock each day, a tradition that continues. The ball, constructed of wood, covered in zinc, and weighing 90 kilograms, as well as the operating mechanism were made by Maudslay, Sons and Field of Lambeth, who also made the time ball mechanism for the Greenwich Observatory. It was installed by James Ritchie and Son (Clockmakers) Ltd, who still maintain it to this day on behalf of Edinburgh’s City Council. (There is an untrue myth that the original ball was much heavier, at 762 kilograms, in part perpetuated by Smyth himself!)

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Nelson Monument – Museums and Galleries Edinburgh

Photograph of the National Monument, Nelson Monument, and City Observatory on Calton Hill in the background

National Monument, Nelson Monument (tall tower) and City Observatory from the North (Wikimedia Commons)