We sometimes imagine the past as a time without clocks, when everything moved at a much gentler pace. Of course, life is not as simple as that, and there have been many historic situations in which people needed to find ways to keep to a busy schedule. For instance, the Greek philosopher Plato (427–347 BC) wanted a way to get himself and his students out of bed in time for lessons. As a result, he became the inventor of the alarm clock.
Simple water clocks – in which the gradual drip of water into or out of a vessel is used to record the passing of time – had been in existence in Babylon and Egypt by the sixteenth century BC. It is also possible that such clocks were used earlier in India and China, as long ago as 4000 BC. The innovation in Plato’s water clock was that it also featured an alarm. A vessel was gradually filled with water, until it reached the height at which a tube led out of the first vessel into a lower receptacle. The tube functioned as a siphon, meaning that as soon as water started to drain out through it, the rest of the water was sucked into the tube with it. As a result, all of the water was instantaneously dumped into the lower receptacle. This lower receptacle was almost completely enclosed, except for a few small openings designed to act as whistles when air was forced through them – which happened when the water fell. So Plato’s students were woken up, along with their teacher, by a loud whistling noise emanating from the extraordinary alarm clock.
Other early alarm clocks worked in similar ways. One involved a vessel that filled with water until it became heavy enough to fall and clatter onto a table below, making a loud noise in the process. Another design used a candle with a metal ball embedded in it, which burned down until the wax around the ball melted and fell onto a metal surface.