Time Gun-Maps

For over 140 years, a cannon has has been fired from the ramparts of Edinburgh castle to signal the time at 1pm.

Time-Gun maps were published in 1861 and 1862 for the Post Office Directory by W & AK Johnston, Geographers and Engravers to the Queen.

These maps let the people of Edinburgh know the time taken for the sound of the one o'clock gun to travel from the gun at Edinburgh castle across Edinburgh.

 

Map  -  Heading

The heading on the 1861 map was:

Hislop's Time Gun Map of Edinburgh

Communicated by Mr Hewat, as prepared for the Time-Gun Subscripton Fund by Professor C Piazzi Smyth, Astronomer Royal for Scotland

The heading on the 1862 map was:

Hislop's Time Gun Map of Edinburgh

(The Gun, a large cannon in the Half-Moon Battery, at the Castle, is fired off at the precise instant of 1 o'clock PM, Greenwich Mean Time, daily, Sundays and holidays excepted, through the agency of electric influence from the Royal Observatory on the Calton Hill.)

Communicated by Mr Hewat, as prepared for the Time-Gun Subscripton Fund by Professor C Piazzi Smyth, Astronomer Royal for Scotland

The tradition of firing the 1 o'clock gun from Edinburgh Castle continues today.  Several different guns have been used over the past 140 years.   Some with a far more powerful charge than is used today.

The gun is also used several times each year to fire 21-gun salutes.

Map  -  Footnotes

At the foot of the 1861 Time-Gun map there was a note:

For every additional circle of distance from the Castel, subtract one second from the instant of the report of the "Time-Gun" to give the exact moment of
1 o'clock

At the foot of the 1862 Time-Gun map were two notes, including quite a long sentence of explanation for note 2.

1.  For every additional circle of distance at which the observer may be from the Castel, he should subtract one second, due to the measured rate at which sound travels, from the instant at which he hears the REPORT of the Time-Gun in order to obtain the exact moment of the fire; or, 1 o'clock.

2.  The FLASH of the Time-Gun's fire, whenever it can be seen, requires, owing to the immense velocity of light, no correction for any distance;  and is otherwise arranged by the manner in which the electricity is made to act, so as to occur true to the tick of the 60th second of the Regulated Normal Clock of the Royal Observatory on Calton Hill, both Summer and Winter, without the loss of the smallest appreciable fraction of a second:  and the said clock being, from hour to hour carefully adjusted in accordance with astronomical observations kept up at the observatory, both by night and by day, shows always the true time, as close as it can be ascertained, by human means.

 

 

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