Eiffel Tower sends time signal to ships

In 1910, the Eiffel Tower began broadcasting a daily time signal that allowed ships in the middle of the Atlantic to know the exact time in Paris, even without undersea cables. This innovation used early radio telegraphy to provide a vital reference for sailors.

Time signal range varies by time of day

The signal from the Eiffel Tower could travel up to 5,000 kilometers at night, compared to about 2,600 kilometers during the day. This difference was due to how radio waves propagated more effectively in the darkness, helping ships correct their chronometers and avoid positioning errors.

Scientific request leads to time service

The idea for the time signal came from the Bureau of Longitudes in 1908, which wanted to improve the precision of global positioning. However, the Eiffel Tower was originally scheduled to be dismantled by the end of 1909, until its use for radio telegraphy became strategically important.

Collaboration between science and military

The Paris Observatory provided the precise astronomical time needed for the signal, while the military radio telegraph service, under Gustave Ferrié, ensured the broadcast. Six cables connected the top of the Eiffel Tower to an underground laboratory, enabling the transmission of the time signal.

Radio wave behavior affects signal reach

Engineers observed that radio waves traveled further at night, a phenomenon they did not fully understand but used effectively. This meant ships far from European coasts might need to wait for the nighttime signal to get a reliable time reference.

Time signal improves maritime safety

Before radio, sailors relied on chronometers that could drift over time, leading to positioning errors of several dozen kilometers. The Eiffel Tower’s time signal allowed ships to adjust their chronometers quickly, making navigation safer and more accurate.

Legacy of the Eiffel Tower’s time signal

The Eiffel Tower’s time signal, broadcast for decades, became a universal and free temporal reference for maritime navigation. It laid the groundwork for modern global time services and improved safety at sea long before the advent of satellites.