How do you know how much a kilogram of coffee is? You probably use a scale. But how do you know all scales are the same? How do you know my scale and the scale used by Colombian sellers are the same? Fortunately there is a list of standard measures (including for example how long, heavy or hot something is) that keep all of us under the same standard. In this new post I will talk about the story behind the measures we all use nowadays. You may think I have gone way out of my field and you are probably right. But I just can't imagine any form of Economics without measurement. And I can't imagine measurement without thinking about the beautiful metric system.
Most definitions of these measures are actually quite complicated. For example, what is a second? The Bureau International des Poids et Measures defines is as:
Before then measures were based on Charlemagne’s ideas. Many were simply borrowed from human body, like the pied du roi (or king’s foot) or the toise (the distance across a man's outstretched arms). But what if men were bigger in one part of the world than in another? Hence measure were quite uncertain and clearly not fixed: they varied from town to town, between occupations as well on the type of object to be measured. So agreements on measures were hard.
What gave room to the Metric System we have today? An economic crisis of course. The famine of 1780s meant that food should get more expensive. But bakers were worried about increasing prices (lots of revolts were happening), so they started baking smaller loaves. People started noticing loaves were smaller, but no one could universally check their weight! And the French revolution set the reform environment which started with a new standard. They wanted a system based on nature, that avoided national vanities and could be used by all nations.
And so first came the meter: They took a quarter of the circumference of the Earth and divided it by 10 million. That's a meter. And this gave birth to the kilogram. To define the unit of mass they preferred water to other bodies (such as gold) because it was easy to get anywhere in the world. They divided the meter in 10, formed cubes of that size, filled them with water and voila! The kilogram. And from the kilo they defined other 4 base units...
This object in France makes sure that whenever I buy one kilo of bread from a shop, we can all agree how much that is. Well, unless you go to typical corner store where a kilo of bread may be less than a kilo. But even in that case we can actually determine the real weight and formally complain about it. This is supposedly the story of Poincare (also in France but in the 1900s). From Allen Downy's Think Stats book:
Let me finish with the story of the first kilogram. This "perfect" object has been used as a prototype to build a few other kilogram sub-prototypes (called sisters) over the world. And these have themselves being used to build others, all the way to our day to day scales. Every time each one of us checks his own weight, this can be traced back to this little object in Paris from the 18th century. And the most interesting thing is that recently it was found that (comparing it to its sisters) the perfect kilogram was losing weight! The funny thing is that even though it lost weight - since itself defines weight - the object is actually still one kilogram! Which brings us to the bummer conclusion that we have all gained weight in the meantime. As the definition of a kilogram got lighter, we all got heavier.
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