May 17, 2016

World Metrology Day

Well, it`s that time again.  World Metrology Day 2016!  May 20’th...a day where we celebrate the signature of the Metre Convention way back in 1875.

To be honest, I didn’t know much about the history of this momentous day until I did some research myself, and it’s really quite interesting...if you’re a Metrology geek like me.  I’ll save you some time and give you all a somewhat brief history here.

The SI unit we all use today dates back to 1215, when the Magna Carta (Latin for The Great Charter) defined the standards of measure which were to be used throughout England.  I’m sure you don’t have hours to read the full story so sticking to the milestones, we’ll just jump forward almost five centuries to 1707, when England and Scotland united into a single kingdom, and the Scots agreed to adopt the same units that had been in use by England for almost 500 years...then, some time later (in the Eighteenth century) Peter the Great, Czar of Russia, adopted the same standards to facilitate trade.

??? Did you know that abuses of measurement units was one of the causes of the French Revolution?  Who knew?

In 1789, a National Assembly was held, where one of the items on the agenda was the reform of measurement units.  What came out of this was the introduction of the metre and the kilogram and the formation of the metric system, leading to the eventual manufacture of prototypes.

Between 1850-1870, many other countries adopted the metric system including Spain, several South American republics and many of the Italian and German states.  The Netherlands, however,  had already adopted the metric system back in 1817.  Another milestone, in my opinion, was the International Postal Union adopting grams as their unit of measure for weights of letters in 1863.

Jump back slightly to sometime in the 1860’s, when it was discovered that there was not only wear evident on the standard metre bar, but that it had a tendency to flex during use, which cast doubt on the reproducibility of the metre and the kilogram.  Napoleon III took this opportunity to try and create his own standard and invited scientists from around the world to attend a conference in Paris...which proved to be bad timing.  Two weeks before the conference, the Franco-Prussian War broke out, France was defeated, Napoleon went into exile, and the newly unified nations of Germany and Italy adopted the metric system.  One problem though...the prototypes of the metre and kilogram were under the control of the Third French Republic.  Problem?  Nah.  The new republican government re-issued invitations and in 1875 scientists from thirty European and American countries met in Paris.  The main focus was the replacement of the existing metre and kilogram, since the existing standards were deemed unreliable and may not be the same as when they originally adopted the system in 1799.  Apparently, French politicians feared the metric system would be rejected, since the existing metre was 0.03% (300 µm) shorter than the design length.  I’m still scratching my head as to how they measured 300 microns back then...  Anyway, in the end, it was decided that the new standards be manufactured as closely as possible to the values of the existing artifacts.

The new prototype metre was the same length as the original one, but the newly manufactured bar had an X cross section rather than rectangular, to reduce the tendency to flex while in use.  In addition to this, it was made a little longer and lines were engraved exactly one metre apart to eliminate the wear issue on the end faces.

The official metre was retained as the international standard until 1960 when, get this, it was redefined in terms of the wavelength of the orange-red line of krypton-86...wait, what?  Seriously?  Apparently, all you need is the equipment to heat a sample of krypton-86...OK, no biggie, I think I have some in my crawl space somewhere. Then, just look for the reddish-orange line produced...simple so far, right?  Oh ya, there it is...I see it.  Next, get out your calculator.  Final step...just multiply the width of that orange-red line by 1,650,763.73 ...and voila, there’s your metre!  Simple enough, right?

Now, before you start questioning how the heck someone came up with that...come to think of it, didn’t the government dabble in LSD experimentation around the same time?  No matter, it’s since changed...phew!  This definition for the meter only lasted until 1983. Scientists then decided to define a meter by how fast light travels in a vacuum. Now this makes more sense to me!  This system is even more exact than the one based on krypton-86.

What about the kilogram you ask?  In 2014 after the 25th CGPM (General Conference on Weights and Measures), the prototype kilogram was still in use. It is expected to be replaced by a new definition within the next few years, though not before the next CGPM in 2018.

Now that we’re somewhat up to date on the evolution of the metric system, you can see just how how important the standardization of a common unit of measure was, and is today.  The science of measurement plays a pivotal role in almost everything we do in today’s society.  Everything we rely on and take for granted in today’s society would not be possible without a standardized method of weights and measures.  Try to think of something that doesn’t rely on this system in some way...I bet you can’t :)

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