| Revision as of 18:57, 20 November 2004 editParanoid (talk | contribs)Extended confirmed users3,204 editsNo edit summary← Previous edit | Revision as of 03:12, 13 December 2004 edit undoGene Nygaard (talk | contribs)Extended confirmed users90,047 edits →Reasons for redefinition: explaining whyNext edit → | ||
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| ==Reasons for redefinition == | ==Reasons for redefinition == | ||
| Does anyone know why the litre was redefined in 1901? It doesn't make any sense to me, when you had a perfectly good definition based on the metre. ] 18:57, 20 Nov 2004 (UTC) | Does anyone know why the litre was redefined in 1901? It doesn't make any sense to me, when you had a perfectly good definition based on the metre. ] 18:57, 20 Nov 2004 (UTC) | ||
| ::It was indeed rather senseless, IMHO, but the CGPM did finally come to their senses and "abrogate" that definition (that's how it is phrased in the legalese of their resolution). | |||
| ::Originally, it was intended that the gram should be the mass of a cubic centimeter of water; so obviously the length standards were constructed first. But then, way back in 1799, the original platinum cylinder known as the Kilogramme of the Archives was constructed by the French government to serve as the mass standard. Since then, the definition of the kilogram has never been officially based on water. | |||
| ::After the Metre Convention (or Treaty of the Meter) of 1875, the organizations known as the CGPM and BIPM were formed. They has a new set of international standards for the metre and the kilogram constructed, placing them in use in 1889. In constructing this new platinum-iridium International Prototype Kilogram and its siblings which serve as national standards, the target was the old French standard—not water. | |||
| ::But by then, in the late 19th century, people had been able to make better measurements of the density of water, at its maximum density and throughout the temperature ranges of liquid water, and were well aware of the discrepancies between the actual kilogram, and what it would have been if the 18th century French technicians had been able to carry out these measurements more precisely in constructing their kilogram. | |||
| ::Obviously, there were some users in the science who thought it was terribly important to have that exact relationship with water at its maximum density. So the CGPM let itself be talked into this hairbrained scheme of redefining the litre to make that true (I wouldn't call it that in the article, but am expressing my opinion of it here on the Talk pages). | |||
| ::Note that this is a flip-flop of the original intention of defining the unit of mass based on the cube of the unit of length. In 1901, they instead redefined the unit of volume based on the unit of mass. | |||
| ::Cubic centimeters, of course, remained the cube of the length units. So for a couple of generations or so, we students had to waste a lot of time learning that they were not the same thing as milliliters. Never mind that there had only been a handful of measurements in the history of the world where it ever made any difference. | |||
| ::There was, of course, a similar discrepancy in the construction of the original metre, from their very good but not as good as today's efforts to measure the meridian quadrant, and as a result there are actually 10.002 Mm from the equator to the poles, rather than the intended 10 Mm exactly. Fortunatly, the CGPM never got talked into any scheme to add another new length unit to use alongside the metre, but equal to 1.0002 m. | |||
| ::Note that I have removed an erroneous claim in the article as I found it that the intent in 1901 was that the 1901 definition would be the same as a cubic decimetre. It was well known that it would not, and that in fact was the entire purpose of that redefinition, to make it different from the cubic decimeter which for water never quite gets up to that 1.00000 kg level under one atmosphere of pressure, even at maximum density. ] 03:12, 13 Dec 2004 (UTC) | |||
Revision as of 03:12, 13 December 2004
See http://www.npl.co.uk/npl/reference/international.html for 1979 acceptance of L as well as l. Hotlorp 23:29 Feb 14, 2003 (UTC)
The year of 1901 cannot be right, can it? I thought the Imperial gallon being defined by so and so measure of water was inspired by the metric definition of a litre, so it must have been at the start of the 18th century -- Egil
You are right: the litre is older than 1901. See the current article. -- Heron
Added kilolitre - my water bills in Australia used to measure consumption in kilolitres. - David Gerard 12:54, Jan 28, 2004 (UTC)
Circular dependency?
Nothing depends ON litre, so no matter what litre depends on, there cannot be any circular dependency, can it? --Mormegil 10:21, 10 Aug 2004 (UTC)
- Good point, removed this from the article. Paranoid 18:57, 20 Nov 2004 (UTC)
Reasons for redefinition
Does anyone know why the litre was redefined in 1901? It doesn't make any sense to me, when you had a perfectly good definition based on the metre. Paranoid 18:57, 20 Nov 2004 (UTC)
- It was indeed rather senseless, IMHO, but the CGPM did finally come to their senses and "abrogate" that definition (that's how it is phrased in the legalese of their resolution).
- Originally, it was intended that the gram should be the mass of a cubic centimeter of water; so obviously the length standards were constructed first. But then, way back in 1799, the original platinum cylinder known as the Kilogramme of the Archives was constructed by the French government to serve as the mass standard. Since then, the definition of the kilogram has never been officially based on water.
- After the Metre Convention (or Treaty of the Meter) of 1875, the organizations known as the CGPM and BIPM were formed. They has a new set of international standards for the metre and the kilogram constructed, placing them in use in 1889. In constructing this new platinum-iridium International Prototype Kilogram and its siblings which serve as national standards, the target was the old French standard—not water.
- But by then, in the late 19th century, people had been able to make better measurements of the density of water, at its maximum density and throughout the temperature ranges of liquid water, and were well aware of the discrepancies between the actual kilogram, and what it would have been if the 18th century French technicians had been able to carry out these measurements more precisely in constructing their kilogram.
- Obviously, there were some users in the science who thought it was terribly important to have that exact relationship with water at its maximum density. So the CGPM let itself be talked into this hairbrained scheme of redefining the litre to make that true (I wouldn't call it that in the article, but am expressing my opinion of it here on the Talk pages).
- Note that this is a flip-flop of the original intention of defining the unit of mass based on the cube of the unit of length. In 1901, they instead redefined the unit of volume based on the unit of mass.
- Cubic centimeters, of course, remained the cube of the length units. So for a couple of generations or so, we students had to waste a lot of time learning that they were not the same thing as milliliters. Never mind that there had only been a handful of measurements in the history of the world where it ever made any difference.
- There was, of course, a similar discrepancy in the construction of the original metre, from their very good but not as good as today's efforts to measure the meridian quadrant, and as a result there are actually 10.002 Mm from the equator to the poles, rather than the intended 10 Mm exactly. Fortunatly, the CGPM never got talked into any scheme to add another new length unit to use alongside the metre, but equal to 1.0002 m.
- Note that I have removed an erroneous claim in the article as I found it that the intent in 1901 was that the 1901 definition would be the same as a cubic decimetre. It was well known that it would not, and that in fact was the entire purpose of that redefinition, to make it different from the cubic decimeter which for water never quite gets up to that 1.00000 kg level under one atmosphere of pressure, even at maximum density. Gene Nygaard 03:12, 13 Dec 2004 (UTC)