Gabriel Mouton
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Gabriel Mouton (1618 – 28 September 1694) was a French abbot and scientist. He was a doctor of theology from Lyon, but was also interested in mathematics and astronomy.

His 1670 book, the Observationes diametrorum solis et lunae apparentium, came to form the basis of what was to become the metric system hundred years later. Based on the measurements of the size of the Earth conducted by Riccioli of Bologna (at 321,815 Bologna feet to the degree), Mouton proposed a decimal system of measurement based on the circumference of the Earth, explaining the advantages of a system based on nature.

His suggestion was a unit, milliare, that was defined as a minute of arc along a meridian. He then suggested a system of sub-units, dividing successively by factors of ten into the centuria, decuria, virga, virgula, decima, centesima, and millesima.

The base unit would be the virga, 1/1000 of a minute of arc, corresponding to 64.4 Bologna inches, or ~2.04 m. This was reasonably close to then current unit of length, the Parisian toise (~1.95 m) – a feature which was meant to make acceptance of the new unit easier.

For practical reasons, Mouton suggested that the actual standard be based on pendulum movement, so that a pendulum located in Lyon of length one virgula (1/10 virga) would change direction 3959.2 times in half an hour. The resulting pendulum would have a length of ~20.54 cm.

His ideas attracted interest at the time, and were supported by Jean Picard as well as Huygens in 1673, and also studied at Royal Society in London. In 1673, Leibniz independently made proposals similar to those of Mouton.

It would be over a century later, however, that the French Academy of Sciences weights and measures committee suggested the decimal metric system that defined the meter as, at least initially, a division of the circumference of the Earth. The first official adoption of this system occurred in France in 1791.

By today’s measures, his milliare corresponds directly to a nautical mile, and his virga would by definition have been 1.852 m.

“This gives us the clue that in his essay, Wilkins was looking at concepts rather than exact measurements, otherwise why would he have stated that the length of the pendulum would be 39¼ inches? One should therefore resist the temptation to draw conclusions from calculations performed to micrometric accuracy. ”

Wilkins didn’t discuss the pendulum, but a string and a ball. From what he describes, the Standard (=metre) would = (L+r) + 0.4r^2/(L+r), where L is the length of the string, and r is the radius of the ball.

Using the method Wilkins mentioned, what would you calculate the Standard (=metre) to be? Maybe much closer to 1.000……

“No matter which country thought of it first, we still can’t deny the fact that the imperial system was used by a majority of people in the UK for hundreds of years.”

Wrong! Imperial came into existence in 1824. That is less then 200 years ago.

And so what if they did use some archaic mumbo-jumbo back then. They also rode in horses, took baths once a month, if that, couldn’t read & write, etc, and mostly lived in poverty. Most of us would not trade places with them.

We have progressed in every facet of life, including weights and measures.

“Another fact that can’t be ignored is that a lot of people still use the imperial system, be it on the roads,”

Because they are FORCED to. Change the signs and see how fat imperial becomes either forgotten or confused. Why is it that those opposed to metric can only come up with road signs and pints in pubs as examples of Fred Flintstone units (FFU) still in use? People also use metric when buying petrol and thousands of products that are marked only in metric in the shops. If you work for a living their business will be metric and they will use it there.

“or talking about their height and weight. Out of all the people I know, none of them tell me their height in metres.”

I’m sure that people’s statistics are a constant source of talk. I can’t remember how long it has been since I was asked how tall I was or even bothered to ask someone. Since I use metric and have a feel for it (none for FFU), I can easily look at someone and tell their height precisely. I don’t have to ask.

1) The “vibration� to which Wilkins referred was the time for the pendulum to swing from one extremity of its motion to the other extremity – ie half of its period.

2) Using a value of 9.8118 m/s² (the value for London), the length of such a pendulum would be 0.9941 m or 39.14 inches.

This gives us the clue that in his essay, Wilkins was looking at concepts rather than exact measurements, otherwise why would he have stated that the length of the pendulum would be 39¼ inches? One should therefore resist the temptation to draw conclusions from calculations performed to micrometric accuracy.

It rewrites the history of the metric system in the sense that John Wilkins as well as Gabriel Mouton are fathers of the system. Wilkins recognised three key things that are important for todays international system (SI):

a) the need to base units on a natural constant rather than an object
b) the need to use a single numeric base of the units
c) the need of international standardisation

I disagree with this. John Wilkins states that his “standard” (= metre) should be equal to 38 Rheinland Zoll (=inches) which is the same as 39.25 British inches. According to this website: http://home.fonline.de/fo0126/geschichte/groessen/mas7.htm, before 1816, the Rheinland Fuss was 0.31385 m. This means the Rheinland Zoll was 26.154 mm.

38 Rheinland Zoll x 26.154 mm/Zoll = 993.86 mm. 39.25 inches, using the post 1959 definition of 25.4 mm per inch yields 996.95 mm. The two values that John Wilkins assumed to be the same vary by 3.09 mm.

This brings a dilemma that results from assuming that a British inch of 2007 (post 1959) is the same length as the British inch of 1668. Do we know for sure how long a British inch was in 1668? Do we know how long a Rheinland inch was in 1668? Is John Wilkins correct in stating that 38 Rheinland inches was equal to 39.25 British inches in 1668? Maybe at that time that relation was true. But the interesting thing is, we don’t know today how much each inch changed since then. If we assume that John Wilkin’s “standard” of 1668 was indeed equal precisely to the metre of today (maybe he knew something the French didn’t know 120 years later and we still don’t know today that would have spared them the need to survey the meridian), then the Rheinland Zoll of 1668 was equal to 26.315 8 mm and the British inch of 1668 was equal to 25.477 mm.

This makes the Rheinland inch longer by 0.1618 mm in 1668 compared to 1816 and the British inch shorter by 0.077 mm from 1668 compared to today. Actually not much of a difference. But still it is just to point out that you can’t assume the inch of today was the exact same length in 1668 and that John Wilkin’s standard varied by 3 mm from the present metre.

I believe in 1668 the inch of London was defined as 3 Barley Corns round and dry. There is no way the Barley corn method could be precise and even a variation of 0.1 mm between Barley Corns would result in a 4 mm variation in 39 inches compared to one metre. This is enough to prove that it is impossible to say the “standard” proposed by John Wilkins is 997 mm. The best we could do is say it was the same as the present metre plus or minus a few millimetres here and there.