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Time Gun-Maps |
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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.
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Map -
Heading
The heading on the 1861 map
was:
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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:
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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. |
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Map -
Footnotes
At the foot of the
1861 Time-Gun map there was a note:
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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.
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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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