18 Jul A Metre in History
In the Discovery team we often talk about the different types of scientists: a botanist, astronomer, palaeontologist and so on. I learnt about a new one recently…that a metrologist is a measurement scientist, someone who studies the science of measurement and how it can be applied.
Image: Official engraved marble standard metre at the Place Vendôme in Paris (Mètre Étalon Place Vendôme). Source: WikiCommons – Author: Chabe01
It’s strange to think that someone invented a metre, the measurement we use every day. It is so useful because it is a universal measurement, one that has the same definition all over the world, and other metric measurements are based upon it.
The story of its invention begins in pre-revolutionary France, when the village you lived in and the work you did determined how you measured things – at that time there may have been 250,000 different units of measurement! Confusing! Many were left over from the Roman occupation centuries before. Even earlier, in the 21st century BCE, the Egyptians recognised the importance of precision measurements. However, like other original measurements, they were based on human lengths, such as the length of a king’s arm, which of course changes substantially from person to person.
So, to skip forward in time to after the French Revolution, the new French Republic decided that as part of a fair world order, not based on religion or royalty, measurement should be based upon the properties of nature and science. After much deliberation, mathematicians and scientists decided upon a base 10 system, the ‘metre’, from an Ancient Greek word ‘metreo’, meaning ‘to measure’. They decided it should be the length of the Paris Meridian (a line between the north pole and the equator, through the Paris Observatory) divided into 10 million pieces. However, working out that length was an enormous task; it took two astronomers seven years, and all sorts of challenges, including high mountains, navigation issues and accusations of spying. They didn’t physically measure the whole length, but a segment of that line and extrapolated it. Once the metre length was determined, several examples were put on display, in places like the side of buildings, so that the public could become familiar with the new length.
150 years ago, in 1875, the Metre Convention was signed by 17 countries, and copies of the metre bar were sent around the world. They remained the international ‘standard’ measurement for decades. Over time, other countries joined the convention, including Australia in 1947. Other measurements were added, such as those for electricity and light, creating the International System of Units (SI).
Image: pexels – Antoni Shkraba Studio
Progress in science meant that distance could be measured in wavelengths, so in 1960, a new definition was applied: a metre is 1,650, 763.73 wavelengths of a particular orange light. Today, time is the most accurate measurement, and so the metre is now defined as the distance that light travels in a vacuum in 1/299792458 of a second. Amazingly, this number is only fractionally different to the original French astronomers’ calculation!
As technology has become more complex, the accuracy of measurements has become more precise. We now measure to billionths of a metre, nanometres, using lasers.
Back to our daily use of measurements and why a uniform system is important: even if you are cooking, measurements such as cups and tablespoons can vary depending on where the recipe comes from (for instance, the UK, or the US). If you use millimetres and grams, the SI, it is unambiguous, and if your recipe is too salty or has not enough yeast, the inaccuracy is likely to be your own!