Developing measurement standards

It will possibly be my last book, but Not Your Usual Science is going to be HUGE, close to 1.5 million words, equal to a dozen 'airport books', the thick tomes you buy to read on a long flight. It collects together many of the articles and essays that I have generated over the past 35 years, covering science, how science works and how what we now call science was put together. It even includes some of the blog entries that have appeared here. In due course, it will be released as an e-book.

Here's a small taste of it...

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In early human societies, the main needs were for standard fair measures for length, weight and volume. With those sorted, you could measure out food, drink, cloth, and most of the other products early humans wanted to trade with each other.

If the trades were to be fair, all measures had to be the same, and this meant comparing them back to a common standard that all people could reach. But even at the heights of the Roman, Mongol and Inca Empires, the fastest messenger service could only cover between a hundred and a hundred and fifty kilometres a day.

Freight carriers and ordinary folk, travelling on foot with a load, would only travel about thirty kilometres a day, or perhaps fifteen if they were travelling with stock. So copies of the standards for weight and length either had to be distributed widely, or they had to be established locally. In most cases, people just set up their own local standards.

Typically, they would use the local ruler’s body, so a digit was the width of the king’s finger, and a cubit was the distance from the king’s elbow to the tip of his longest finger.

Obviously this sort of thing makes problems: what happens if the throne is taken over by a midget? Or a giant? Obviously people needed a better standard, preferably an international one, so measurements no longer had to be given in London inches, or Paris inches.

The foot is a convenient sort of unit, and so is the inch, and even the yard has a comfortable sort of feel about it. In the end, when the French Revolutionaries did away with their monarch, they changed the units as well.

The basis, they proposed, would still be about the same as one yard, but it would be defined in a non-human, international way. It was to be one ten-millionth of the distance between the North Pole and the Equator on a meridian passing through or near Paris, Dunkirk and Barcelona. (They chose that meridian, because a ten-degree length of it had just been accurately surveyed, between 1792 and 1799.)

This measurement system was known as the metric system, and it is more or less what we use today. We now call our measurement system SI (for Système Internationale), and the metre is now defined from the speed of light, now defined for all time as 299,792,458 metres per second, with the second defined by a special clock called a caesium clock.

These are standards any large laboratory in the world can reproduce whenever they want to. The standard international kilogram used to be a platinum-iridium cylinder, stored at Sèvres, near Paris, between 1889 and November 2018. On the latter date, a new standard was announced, to apply from May 2019.

The change was forced because the standard cylinder had lost about 50 micrograms over the past 130 years. Now the world will use a value of Planck’s constant. This will be 6.62607015 × 10^-34 m² kg/s, and for valid reasons, that now sets the mass of the kilogram totally.

Now back to the French Revolution: why were the French so keen on new standards? Maybe it had something to do with the three different standards of length in use in just one city, Bordeaux, in 1800. In a case like this, it would pay to shop around before you bought anything, and maybe the people of Bordeaux felt they were wasting too much time!

We certainly know that the lack of standards annoyed the nobles of Norman Britain. When they assembled to meet with King John, they placed this passage in the Magna Carta:

Throughout the kingdom there shall be standard measures of wine, ale and corn. Also there shall be a standard width of dyed cloth, russet, and halberject; namely [a width of] two ells within the selvedges. Weights [also] are to be standardised similarly.

From 1215 until now, the process of standardisation has been slow. It was only a generation ago that the United States inch (2.54005 cm) and the British inch (2.5399956 cm) were brought into line with the Canadian and Australian inch (2.54 cm).

So even where the metric system is not used, the “local” units are tied to the international metric standards, and the era of local units has almost passed. Mind you, with the loss of those units, a great deal of romance has passed away as well, but that assertion requires illustration.

Early English units for measuring liquid started with the mouthful, which was about 15 millilitres. Twice this was a jigger or handful. Two handfuls made a jack, or jackpot, and two jackpots made a gill, or jill.

When Charles I needed more money, he placed a tax on the jackpot, and reduced its size, so there would be more of them. The gill was (by its definition as two jackpots) also reduced in size, much to the annoyance of the common people.

The pail was another measure, about the size of a gill. Given that King Charles wore a crown, until he was beheaded a few years later, you may now be able to read the old rhyme about Jack and Jill with more understanding. Just one question remains unanswered: was Jack anything to do with the Jacobites, who took their name from the Latin form of James, Jacobus?

Just to finish the sequence of old liquid measures, two gills made a cup, and two cups a pint. There were two pints to the quart; and two quarts made a pottle; while twice a pottle was a gallon. The double gallon was also called a peck; the double peck was a half bushel; and obviously two half bushels made a bushel, which was eight gallons, or about 35 litres. Two bushels filled a cask; and two casks made a barrel or chaldron. Doubling the barrel gave us a hogshead of about 280 litres. 

Some of these terms are still in common use today. And even though we have largely changed over to metric measurements, there are other hangovers from the past as well. The size of the type used in a book is measured in points, with 72 points to the inch.

Wind speeds are still measured in knots (nautical miles per hour), and diamonds are weighed in carats (not to be confused with the karat, which is a measure of the purity of gold.

And you may still have inches on your feet, even if you live in a country which mostly uses metric standards. In the time of Edward I of England, the inch was defined by “three grains of barley dry and round make an inch”. To this day, the difference between a size five shoe and a size six shoe is still just one barley corn, a third of an inch!