It was limited by weather and darkness, and was not at all private. The average speed to transmit a message was two words per minute.
Semaphore was transmitted not only by the above mechanical means, but also by ship flags, Aldis Lamps, Heliographs and hand held flags. The last semaphore commercial station closed in 1880, in Sweden.
After looking at the single needle telegraph alphabet code (right) you can soon detect that when the needle deflects to the left it is equivalent to a dot and when it deflects to the right it represents a dash. It was deflected by a positive or negative current to cause the required result.
The town of Semaphore, 9 miles from Adelaide is a contemporary reminder of its use. But in Tasmania human as well as shipping movements were tracked by the device. Until 1846 a chain of semaphore stations dotted the Tasmanian Peninsula. Convicts attempting to escape from the fiercely guarded penitentiary at Port Arthur knew the system to their peril. From the strategic heights of Mt Cunningham, Eaglehawk Neck, Mt Raoul and Mt Nelson to Hobart town, messages of their sighting could be transmitted from Hobart to Port Arthur in under 15 minutes. There were however, several drawbacks to this optical telegraph's use, despite its historical adoption in peace and war.
Rain, fog, mist and snow, dimmed its power. It was labour intensive and totally ineffective at night. It was the electric telegraph that would transform the business of communication in Australia and bring mercurial speed to the flow of news, information and human exchange that underpinned the structures of a rapidly advancing society.