Metrication matters - Number 23 - 2005-04-10
Metrication matters is an on-line metrication newsletter for those actively involved, and for those with an interest in metrication matters.Help a friend – if you know somebody else who can benefit from this newsletter, please forward it to them and suggest that they subscribe. If a friend passed on this newsletter to you, please check the details of the free subscription at the end.
Dear Subscriber,
Contents
1 Feedback - notes and comments from readers 2 Editorial 3 Oddities - measurements from around the world 4 Tips - pointers and methods to make your measurements easier. 5 Signs of the times 6 Quotations 7 Q&A - readers' questions and answers 8 Rule of thumb 9 History 10 Hidden metric
1 Feedback
In responses to the questions, 'What part of 'Metrication matters do you like the best?' and 'What part of 'Metrication matters do you like the least?' in our recent annual reader's quiz there was no particular preference for the various headings we use, so we will retain the present format for the time being.
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2 Editorial
Does this story resonate with anyone in the metrication community?
This is a story about four people named Everybody, Somebody, Anybody, and Nobody who were given the job of metrication. They were told that this was a very important job that to be done smoothly and quickly. Everybody was sure that Somebody would do it. Anybody could have done it, but Nobody did it. Somebody got angry with that, because it was Everybody's job. Everybody thought Anybody could do it, but Nobody realized that Everybody wouldn't do it. It ended up that Everybody blamed Somebody when Nobody did what Anybody could have done!
Adapted from an unknown source. This appeared in the London Financial Times (1998 July 9) where Nigel Rees attributed it to Cassell’s Humorous Quotations, but I have seen several unattributed Google references earlier than that, all of which use some version of 'origin unknown'.
3 Oddities
Over time, I have collected many positive benefits following metrication. Metrication can lead to:
• Better morale
• Getting it right first time
• Greater accuracy
• Greater customer happiness
• Less customer unhappiness
• Less cheating
• Less mistakes
• Less repeating things
• Less staying back to fix things not done right first time around
• Management sleeping better at night
• More happiness
• More harmony
• More honesty
• More pleasant working atmosphere
• More togetherness because we all feel better valued
• People feeling valued because of less niggling over errors
• Shorter meetings
4 Tips
Obviously beer and wine cool faster in your freezer than they do in your refrigerator, but a better way to cool them is in a container of iced water. The water interacts with the bottles or cans more quickly and because the iced water is about 4 °C you cannot over chill your drinks to glass breaking temperatures. Clearly this scientific fact is well known to Australian party goers who use baths and garbage bins full of ice and iced water to cool their bottles and 'tinnies' before a party (Highly scientific these Australians!).
5 Signs of the times
The world is truly becoming more and more international. I was reasonably content when 'Metrication matters' went to readers in English speaking nations such as Australia, Canada, New Zealand, UK, and USA, but I am a little surprised that there are now have readers in such places as Austria, France, Germany, Netherlands, and South Korea.
6 Quotation
He who rejects change is the architect of decay. The only human institution which rejects progress is the cemetery.
Harold Wilson
7 Q&A
Question
I have read that the original metre was based on the size of the Earth, and that now it is based on some property of light. Just exactly how many times has the length of the metre changed?
Answer
Once
The provisional metre of 1795 was changed to the present metre in 1799. The original length of the 'provisional' metre was legally adopted by the French Government in 1795. After the two astronomers Jean-Baptiste Delambre (1749–1822) and Pierre Méchain (1744–1804) finished their survey to find the size of the Earth, the metre was adjusted to suit their new information. That was the only change in the length of the metre.
However, since 1799 there have been several changes in the definition of the metre without any corresponding changes in the length of the metre. The metre is still the same length that it was when it was defined in 1799.
When you read about changing the definition of the metre, this refers to coming up with a better way to define it, while not changing its value. The metre is the same length, but its definition has changed a few times since 1799. Whenever the Conference Générale de Poids et Mesures (CGPM) has redefined the metre, the goal has always been to improve the precision of the definition, but not to change the length of the metre.
Short history of the metre
Initial considerations (1790 May 8)
Following a motion by Talleyrand, the French National Assembly decided on the creation of a decimal system of measurement units that would be stable, unvarying, and simple. The first unit chosen was the metre and its length was to be based on the length of a pendulum beating a second.
Académie des Sciences (1791 March 30)
After a proposal by the Académie des Sciences (Borda, Lagrange, Laplace, Monge and Condorcet), the National Assembly chose that a metre would be a 1/10 000 000 of the distance between the North Pole and the Equator. The main reason that the French Academy of Sciences chose the meridian definition over the pendulum definition was because the force of gravity varies slightly over the surface of the earth, affecting the timing of the swing of the pendulum.
To determine the distance from the North Pole to the equator it was assumed that a portion of a meridian could be measured accurately and the whole distance could then be estimated from this sample. The meridian chosen went from Barcelona in Spain, to Dunquerque in France; this choice was an early example of the intended international nature of the metric system. Two astronomers, Borda and Méchain, were appointed to carry out the measurement.
This definition of the metre never specifically referred to Paris, but many physics textbooks have since claimed that they chose the Paris meridian. Internationalism was an aim right from the beginning so the meridian they chose to measure was supposed to count for all meridians even though the international zero-meridian of longitude is the one that passes through Greenwich near London.
In 1791, it was already known that the Earth was slightly flattened near the Poles. Nevertheless, a North South meridian was chosen rather than the equator because it was valid 'for all people around the Earth' when the Equator only covers a small fraction of humanity'.
The members of the Académie des Sciences reasoned that if the Earth was a perfect sphere, its circumference would be 40 000 km – by definition – as the distance from a Pole to the Equator is 10 000 km.
The definition of the metre has changed throughout time, following the development of science and the constant improvement of measuring tools. The precision of the measurement was thus made more and more accurate, but, to repeat, the length of the metre has not changed since 1799.
First definition (1 Aug 1793)
To have an interim measure before the final standard for the metre could be created an official provisional metre was made from copper by Etienne Lenoir (1744–1822). To familiarize people with the new standard many metre sticks were mass-produced and supplied to citizens. These were used widely for everyday measuring. The length of this metre was based on measurements of the Earth done by César-François Cassini de Thury’s (1714–1784) in a survey he did in 1740.
This is called the 'First legal definition' because On April 7, 1795, the Convention decreed that the new 'Republican Measures' were to be henceforth legal measures in France. This law confirmed the provisional copper metre made by Lenoir as the legal metre.
Second definition (6 Jun 1799)
By 1798, the two astronomers, Delambre and Méchain had completed their measurement of the meridian from Barcelona to Dunquerque. It had taken them six years to measure this line to help them estimate the circumference of the Earth as exactly as possible.
The measurements of Delambre and Méchain were discussed by an international commission in 1799 – this was the first, ever, international scientific conference. This commission decided on the length of the metre and commissioned Lenoir to make the final prototype out of platinum. This became known as the 'metre of the archives' when it was deposited into the Archives of the French Republic on 22 June 1799. This new metre was shorter than the provisional metre by about a third of a millimetre or 325 micrometres to be more precise.
This was the first time in history that the world had a definitive and universal standard of length.
Third definition (1889 Paris Conférence Générale de Poids et Mesures (CGPM)
A new standard metre bar, with an X cross section was made. The length between two lines on the international prototype metre bar was the same as the length of the 1799 metre. The new metre was made from a more stable material – platinum (90 %) and iridium (10%), and was a standard metre length at a temperature of °C.
Fourth definition (14 Oct 1960)
The standard metre bar was replaced by a definition of the metre as 1 650 763.73 wavelengths in vacuum of the orange-red light radiation of the krypton 86 atom (corresponding to the transition between levels 2p10 and 5d5). It is interesting that metal prototypes of the metre had been in use for 167 years from 1793 to 1960 before science and technology had developed sufficiently for them to be replaced.
Fifth definition (20 Oct 1983)
The metre is the length travelled by light in a vacuum during 1/299 792 458 of a second. This is based on the speed of light as c = 299 792 458 metres per second.
The modern definition of the metre has now evolved for more than 200 years; it has done this in a process of continual improvement but without changing its length. To give you an idea of the progress that has been made with the definition of the metre, the most recent definitions fix the accuracy of the original definition of the metre about 100 times more precisely than it was possible with the 1889 definition.
The 1983 definition has been reviewed and adjusted to make it even more precise in 1987, 1992, and 1997. See: http://www1.bipm.org/en/si/history-si/evolution_metre.html for details of these adjustments.
Modern thought by the CGPM recognises that advances in the technology of lasers will lead to new concepts for the definition of the metre. They chose the speed of light as the basis for this standard because this is not based on any particular radiation, so this opens the way for future improvements in the precision of the metre's definition, again and again, without changing its length.
8 Rule of thumb
The Rule of Twice: – for many people this approximation works. Measure the distance around your wrist; twice around your wrist is the same as around your neck; twice around your neck gives your waist measurement – and if this is more than a metre you probably need to do something about it.
9 History
In 1999, to celebrate the 200 years since the first development of the metric system, the French and Spanish governments planted 10 000 trees on the meridian of longitude between Dunquerque in France and Barcelona in Spain. This is the same meridian on which Delambre and Méchain measured the original unit of length, the metre. To celebrate the occasion an enormous picnic was held all the way along this line, now known as 'the green meridian'. Since 'a long lunch' does not translate too readily into alliterative French, perhaps this picnic could be referred to as 'un déjeuner distingué'. (We held our own version of 'a long lunch' at our home in Geelong to celebrate this anniversary. Our long lunch spread – with pushed together tables – from the dining room into the lounge room; it then extended until late in the afternoon!)
10 Hidden metric
When beer drinkers in England order a 'pint' of beer, they actually receive a half litre of beer after allowance is made for the froth that sits on the top of the beer of the 'pint' glass. 'Half a litre of beer, please'.
Cheers,
Pat Naughtin
Geelong Australia
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