Time Signal - Audible and Visible Time Signals

Audible and Visible Time Signals

One sort of public time signal is, of course, a striking clock. These clocks, however, are only as good as the clockwork that activates them; they have improved substantially since the first surviving clocks from the 14th century. For many members of the general public, a public clock such as Big Ben was the only time standard they needed.

When more accurate public time signals were desired for use in navigation, a number of traditional audible or visible time signals were established for the purpose of allowing navigators to check their marine chronometers. These public time signals were formerly established in many seaport cities.

As an example of such a signal, in Vancouver, British Columbia, a "9 O'Clock Gun" is still shot every night at 9 pm. This gun was brought to Stanley Park by the Department of Fisheries in 1894 to warn fishermen of the 6:00 pm Sunday closing of fishing. The 9:00 pm firing was later established as a time signal for the general population. The Brockton Point lighthouse keeper, William D. Jones, originally detonated a stick of dynamite until the Time Gun was installed. A similar "Noon Gun" is still shot every noon at Cape Town, South Africa, as well as at the Citadelle of Quebec. A cannon was shot at one o'clock every weekday at Liverpool, England, at the Castle in Edinburgh, Scotland, and also at Perth in Australia to establish the time. The Edinburgh "One O'Clock Gun" is still in operation. A cannon located at the top of Santa Lucia Hill, in Santiago, Chile, is shot every noon. In places where a cannon is used for a time signal, locals often joke that they can spot tourists because they jump in surprise while locals check their watches. In many Midwestern US cities where tornadoes are a common hazard, the emergency sirens are tested regularly at a specified time (such as, say, noon each Saturday); while this is not primarily intended as a time signal, locals often do check their watches when they hear it.

The first time ball was erected at Portsmouth, England in 1829 by its inventor Robert Wauchope. One was installed in 1833 on the roof of the Royal Observatory in Greenwich, London, and the time ball has dropped at 1pm every day since then. The first American time ball went into service in 1845. Because the speed of light is much faster than the speed of sound, visible signals enabled greater precision than audible ones; however, the audible signals could operate under conditions of reduced visibility. In 1861 and 1862, the Post Office Directory had time gun maps published that related the number of seconds it took for the report of the time gun to reach various locations in Edinburgh. The ceremony of Times Square Ball drop at New Year's Eve in Times Square, New York City, is a vestige of a visual indication of time.

In many non-seafaring communities, loud factory whistles served as public time signals before radio made them obsolete.