Fire destroyed Wellington's time ball on the night of its 45th anniversary, on March 9, 1909, when leaping flames seized the tower of Wellington Harbour Board's J shed on the former Railway Wharf.
When New Zealand's first time ball service began in 1864, the black ball was dropped daily at midday from the mast above the Customs House on Queens Wharf.
J shed's watch tower became the second location for the time ball, from 1888.
The time ball was then dropped weekly at advertised times from the tower of the old galvanised iron and wooden building at the Waterloo Quay entrance of Railway Wharf.
The dropping of the time ball had enabled ships' captains in the pre-radio era of visual signals to adjust their vessels' chronometers while in port.
Safety for a ship and its crew depended on having an accurate knowledge of its true position at sea.
Although latitude had been accurately calculated for centuries, longitude locations could not be easily calculated until the invention of the chronometer in the 18th century.
Chronometers could develop errors of seconds during long sea voyages.
It was essential to verify their accuracy whenever possible to prevent ships' navigators making large miscalculations of distance.
Time ball drops became a popular means for checking the accuracy of chronometers after the world's first time ball station opened in Portsmouth, England, in 1829. It operated on Greenwich mean time.
Captains aboard ships anchored in Wellington Harbour deducted 11 hours 30 minutes from the city's midday time ball drop.
The chronometer readings in front of them would show 12 hours 30 minutes Greenwich time if they were correct.
Accurate time was achieved by astronomical means in the 19th century, when clocks were set while the sun or a star passed the meridian, an imaginary line in the sky that ran from north to south.
Two clocks governed the dropping of the time ball.
The astronomical or second clock gave the true time, in order to set and on occasion correct the clock attached to the battery, which activated the dropping of the black time ball.
The cost of the astronomical clock and its fittings and apparatus was £941.12.7d (about $98,400 now).
As Wellington expanded, the time ball in its original location became increasingly harder to see as buildings dotted the city skyline.
The harbour board favoured relocating the time ball to Mt Victoria, but the Marine Department rejected the idea.
The time ball was eventually moved to Railway Wharf, overhauled on site, and began its drops from the J shed tower on December 28, 1888.
A galvanometer signal from the Dominion Observatory to the Public Telegraph Office replaced the time ball drop after the 1909 fire.
The harbour board built Shed 21 in 1910 on the site where J shed had stood.
A plaque near its Waterloo Quay frontage commemorates the time ball.
- The Wellingtonian