Charles Piazzi Smyth was the instigator of both the Time Ball, in 1853, and the Time Gun, in 1861, for the propagation of time to mariners docked in the Port of Leith, thereby removing the necessity of their bringing chronometers onto Calton Hill to calibrate them against the master clock in the Observatory.
Although the Time Ball was wound up to its top position manually, both the dropping of the ball and the firing of the gun were electrically controlled by the master clock in the Observatory.
The Time Ball was released by a single pulse of electricity that was transmitted by wire at precisely 1PM.
In the case of the Time Gun a slave clock was kept in exact time by electrical pulses passing down a single wire hanging between the Nelson Monument and the Castle ramparts. The gun was fired when the slave clock reached 1PM. The hanging wire was unsupported and at the time, and over 4,000ft long, was the longest single span of wire in the world.
It is a fitting legacy to Charles Piazzi Smyth that we still fire the Time Gun and drop the Time Ball, when in a state of repair, at precisely 1PM daily, Sundays and some Public Holidays excepted.
Dr Bruce Vickery