Clockmakers thus continued to successfully perfect their systems: as early as 1759, John Harrison had made a clock whose precision was a tenth of a second per day! But it wasn’t until 1918 – at least in terms of the principle the actual clock wouldn’t appear until the 1930s – that a new scientific breakthrough occurred: the quartz system. In other words, if the length of the pendulum changes (because of the temperature, for instance), the clock will lose its accuracy the same is true if the acceleration of gravity changes (for example, by gaining altitude). Never mind what it is that oscillates, providing that it is as regular as possible.” In mechanical clocks, the period of oscillation depends on the length of the pendulum and the acceleration of gravity. "A system that oscillates regularly over time. “Ultimately, what’s a clock?” asks Professor Thierry Bastin, director of the Atomic Spectroscopy and Cold Atom Physics Department at the University of Liège. Following Galileo’s work on the pendulum, the 17th century was to experience a decisive advance: the development of the pendulum clock. He then attempted to create instruments capable of objectivising these observations and measuring such intervals: sun dials or sandglasses for instance. As a result, Man turned naturally towards phenomena that showed great regularity such as the earth’s rotation on its axis or that of the moon around the earth. Or, to be more precise, the history of measuring time intervals because that is what we have always measured. The history of measuring time is probably as long as that of humanity. This would be a world first for this type of maser. The aim of the next step is to divide the weight of these devices by ten so that they can be put on board the satellites at a low cost. The first prototype has just been completed. ![]() Professor Thierry Bastin’s atomic physics unit took up the challenge with the Liège-based company Gillam-FEi within the framework of the Walloon “Marshall Plan”. Europe would like to become completely autonomous in this sector, in particular to meet the needs of its Galileo navigation system. The Swiss also market this type of clock, but with a Russian heart. The construction and marketing of high-performance hydrogen maser atomic clocks remains the privilege of the Americans and the Russians.
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