6 ms·

The basis for the metric system was not defined by some arbitrary prototype at first, but by measurements everyone on the planet could reproduce using the sun a

The basis for the metric system was not defined by some arbitrary prototype at first, but by measurements everyone on the planet could reproduce using the sun and a bit of water, at least to a very acceptable approximation. The kilometer was based on 1/10000 the distance between the poles and the equator. The liter was based on the meter, the kilogram was based off the weight of water in a liter, the celcius was based off the freezing and boiling point of water at sea level, etc. The reference meter was put in place to fix the problem arising from the error margin in measurements, but for practical purposes, the definition was all that was needed for a country to join the metric system.

Cockbrand 3y ago
I’ll never stop being fascinated by how neatly all of this fits together: take a hollow cube that has 10cm long edges. Fill it with water - now you have a liter of water. It weighs 1kg. Put it into the freezer, when it just starts freezing, it’s 0°C. Put it onto a stove, and when it starts boiling, it’s 100°C. Simple as that.
- defrost 3y ago
  > Put it onto a stove, and when it starts boiling, it’s 100°C. Simple as that. Not quite - don't forget your elevation | air pressure. Of course not even elevation above mean sea level is straightforward .. what is the MSL of Australia, for example, and how does it relate to the Geoid, the long tidal run through the long narrow straits to the north of Australia, the WGS ellipsoid, etc.
  - jeffchien 3y ago
    Not to mention the dissolved solids as well, so it's not as simple as using tap water. IMHO Celsius is the SI unit least deserving of praise. It's just bolted onto the system through the Boltzmann constant and isn't intricately linked like other SI/CGS units. It's also a little too coarse for modern use. Sure, I could use decicelsius myself, but that doesn't stop every other weather station, AC/thermostat manufacturer, etc. from still using whole degrees. You can buy $2000 Italian espresso machines with elaborate PID controllers that can only be tuned to whole degrees, which ironically means that using Fahrenheit is more precise!
    - triactual 3y ago
      The isotopic content of the water matters too. Boiling point are not used to calibrate thermometers though. Freeze points and triple points are used for temperature calibration. And outside of a primary standards lab, it’s usually just a transfer standard (another, more accurate thermometer).
    - pocketarc 3y ago
      I think there’s some confusion here - the Kelvin is the SI unit of temperature, not Celsius.
    - arlort 3y ago
      Besides Celsius not being the SI unit. I'd be shocked if weather forecasting is ever precise to less than 1-2 °C
      - defrost 3y ago
        > I'd be shocked if weather forecasting is ever precise to less than 1-2 °C That's not a forecast .. actual forecasts for a region are often more accurate than that wrt "mean tempreture" for that region. Where I live the BoM (Bureau of Meteorology) cannot "accurately" predict the upcoming daily tempreture and rainfall for the town that I'm in. They do very accurately predict the mean temp. and rainfall for the wider region. Doppler RADAR gives a very accurate measure of the amount of moisture held by rain bearing clouds, stable wrt broad area winds give a good path for that moisture's travel in the next 12-24 hours, experience + data give solid predictions for the amount of water to be shed, along with bulk cooling from shade and water fall + evaporation. The difficulty rarely lies in the bulk parameters for a broad area, the devil is in the small details which are inherently turbulent. To measure the accuracy of forecasting it first has to be ring fenced by what area you intend to predict the mean attributes for, the timescale you intend to project for, etc.
        arlort 3y ago
        Yes, but all of that is unrelated to the original point The commenter I replied to was complaining about weather stations not using decimals. As you point out we can predict averages with a better accuracy, but services which have that accuracy do use decimals, where decimals aren't used is in consumer weather forecasts where an accuracy of less than 1 degree is anyway useless because > the devil is in the small details which are inherently turbulent
- javawizard 3y ago
  It gets even better: take that 1kg of water at 0°C, add 100 kilocalories of heat energy, and it's now 100°C and just about to boil. (That's assuming you're at sea level, as another commenter noted - if you're at 5,000 feet, the boiling point of water is something like 95°C.)
- akira2501 3y ago
  If you do this at Sea Level when Air Pressure is the barometric mean pressure with nothing but H2O, yes. Otherwise, not exactly, in ways that require formulas to quantify. Metrology is the dirtiest of all sciences, it does not grant simplicity. Anyways.. the counter example was the old definition of the Ampere: "the constant current which, if maintained in two straight parallel conductors of infinite length of negligible circular cross section and placed one metre apart in a vacuum, would produce between these conductors a force equal to 2 × 10−7 newton per metre of length." Perfectly unrealizable within this Universe.
- tzs 3y ago
  It has some warts. A mole of electrons has a charge of about 96487 coulombs. 100000 would have been nicer.
akira2501 3y ago
> the celcius was based off the freezing and boiling point of water at sea level These are not particularly great choices. Water transitions to a solid when it freezes, and distance from sea level has a massive impact on the boiling point of water which Celsius did promptly characterize. Also, somewhat weirdly, Celsius used to be inverted, with 100 being freezing and 0 being boiling.
IvyMike 3y ago
> The kilometer was based on 1/10000 the distance between the poles and the equator. The definition we should have used (and almost did) was that the meter was the length of a pendulum with 1 second swing (in other words, a pendulum with a 2 second period). https://maa.org/sites/default/files/images/upload_library/22/Schwartz.pdf https://maa.org/sites/default/files/images/upload_library/22... If we had done that, the gravitational constant of Earth would be exactly pi^2 m/s^2: Neat, right? https://godplaysdice.blogspot.com/2007/09/why-g-2.html https://godplaysdice.blogspot.com/2007/09/why-g-2.html
- irrational 3y ago
  I wish it had been defined in relation to the speed of light in a vacuum. 299,792,458 metres per second. Set it at 300,000,000 meters per second and derive the length of the meter from that.
  - reaperman 3y ago
    > I wish it had been defined Wish what had been defined? the second?
    - ryanmcdonough 3y ago
      > and derive the length of the meter from that. I would assume they meant meter since they wrote that.
    - irrational 3y ago
      The meter. The distance light travels in a second in a vacuum is fixed. Divide that distance by 300,000,000. That is the length of 1 meter.
      - reaperman 3y ago
        So the current definition is: > The meter (m) is defined by taking the fixed numerical value of the speed of light in vacuum c to be 299,792,458 when expressed in the unit m s−1, where the second is defined in terms of ∆νCs.[0] Your proposed change is keeping this the exact same but changing 299,792,458 to 300,000,000? You said: “I wish it had been defined in relation to the speed of light in a vacuum.” I believe it is already, as written above. 0: https://www.nist.gov/pml/owm/si-units-length#:~:text=The%20meter%20(m)%20is%20defined,terms%20of%20∆νCs https://www.nist.gov/pml/owm/si-units-length#:~:text=The%20m....
qball 3y ago
>The kilometer was based on 1/10000 the distance between the poles and the equator. And that measurement they got was ultimately off, which is why the meter became (until its later redefinition), for all intents and purposes, "the length of some arbitrary metal bar". Clearly, "some fragment of roughly how large the Earth is" is a base unit designed first and foremost for human-scale measurements, and definitely not by self-fellating academics that would never seriously have to use the thing (and whose work does not, by and large, depend on the base unit used; Americans use thousandths-of-an-inch for everything under 1/64th). Fortunately, metric time was too weird even for the French. >but by measurements everyone on the planet could reproduce using the sun and a bit of water, at least to a very acceptable approximation. By contrast, the "foot", which is literally named after the device used to approximate it. The median human being has two of these. In fairness, you usually have to be taught which part of one's body approximates the inch and is thus harder to do. >join the metric system The metric system was initially imposed at gunpoint by the French upon most European nations in the first place due to the French going batshit insane just before 1800 and conquering most of the Continent. The Russians, being a nation that rather famously was not conquered by the French during that time, would retain Arshins until Communism (at which point the Soviets would impose the metric system, also at gunpoint- kind of sensing a theme here); the English would retain the Imperial system even longer than that. It's also why people living in the only nation that really has a choice all measure distance and height in (square) feet, inches, and kilometers (per hour), human weight in pounds (and very rarely ounces), most other weight in grams and kilograms, non-cooking-related volume in liters, and non-cooking-related temperature in celsius. It would have been objectively better from a usability to have just set '1 meter = 1 foot' and call it a day- could have even been (one of) the French foot, too. But no, just had to fuck it up for everyone who actually has to use it because "we know better".
- mathieuh 3y ago
  I never thought I would see an American Exceptionalist comment about a system of measurements. Metric measurements are as intuitive to me as American customary units are to you. I can just as easily use my handspan or the lengths of my fingers to estimate lengths in centimetres as you can in inches. I know without thinking what clothes I should wear when I see the weather forecast in Celsius. I know roughly what temperature I should set the oven to in Celsius based on what I’m cooking. Having grown up in a metric country, American or imperial units mean nothing to me. If I’d grown up in America I’m sure American units would be intuitive for me. The only difference, as you say, is metric is far easier and more intuitive as soon as you want to do anything complicated with those measurements.
tzs 3y ago
> The basis for the metric system was not defined by some arbitrary prototype at first, but by measurements everyone on the planet could reproduce using the sun and a bit of water, at least to a very acceptable approximation. I've got sun here and a well that will give me almost 50 liters/minute of water indefinitely. What measurements do I need to do to get a good approximation of the meter?
- deleted 3y ago
  [deleted]
- eqvinox 3y ago
  Problem is "the planet" is part of the requirements in that sentence too, since the original meter definition was 1/40000 of the circumference of the earth. You don't need to sail around the world for that, you can get it by shadow measurements, but you need measurements from two places on earth at the same time of year/position of the sun. cf. [ https://en.wikipedia.org/wiki/Eratosthenes#Measurement_of_Earth's_circumference https://en.wikipedia.org/wiki/Eratosthenes#Measurement_of_Ea... ]. The result you get from that is knowing what fraction of the earth's circumference is between the two places, which with the 1/40000 definition you can convert to meters. It's certainly doable, but you need the places to be reasonably far apart to get any accuracy, so… more of a "summer road trip" project, but could be fun with kids? ;) To be fair, the entire idea of metrology is that a few people do the work to get primary references and you distribute from there. There's a reason entities like NIST and PTB gets tax dollars.
  - Valgrim 3y ago
    Kids? I would probably have the time of my life organizing an expedition with 5-6 full grown adults where the goal would be to go out there with nothing but our brains and hands, no device or ruler or anything like that, and figure out the length of a meter.

Cockbrand 3y ago

I’ll never stop being fascinated by how neatly all of this fits together: take a hollow cube that has 10cm long edges. Fill it with water - now you have a liter of water. It weighs 1kg. Put it into the freezer, when it just starts freezing, it’s 0°C. Put it onto a stove, and when it starts boiling, it’s 100°C. Simple as that.

defrost 3y ago
> Put it onto a stove, and when it starts boiling, it’s 100°C. Simple as that. Not quite - don't forget your elevation | air pressure. Of course not even elevation above mean sea level is straightforward .. what is the MSL of Australia, for example, and how does it relate to the Geoid, the long tidal run through the long narrow straits to the north of Australia, the WGS ellipsoid, etc.
- jeffchien 3y ago
  Not to mention the dissolved solids as well, so it's not as simple as using tap water. IMHO Celsius is the SI unit least deserving of praise. It's just bolted onto the system through the Boltzmann constant and isn't intricately linked like other SI/CGS units. It's also a little too coarse for modern use. Sure, I could use decicelsius myself, but that doesn't stop every other weather station, AC/thermostat manufacturer, etc. from still using whole degrees. You can buy $2000 Italian espresso machines with elaborate PID controllers that can only be tuned to whole degrees, which ironically means that using Fahrenheit is more precise!
  - triactual 3y ago
    The isotopic content of the water matters too. Boiling point are not used to calibrate thermometers though. Freeze points and triple points are used for temperature calibration. And outside of a primary standards lab, it’s usually just a transfer standard (another, more accurate thermometer).
  - pocketarc 3y ago
    I think there’s some confusion here - the Kelvin is the SI unit of temperature, not Celsius.
  - arlort 3y ago
    Besides Celsius not being the SI unit. I'd be shocked if weather forecasting is ever precise to less than 1-2 °C
    - defrost 3y ago
      > I'd be shocked if weather forecasting is ever precise to less than 1-2 °C That's not a forecast .. actual forecasts for a region are often more accurate than that wrt "mean tempreture" for that region. Where I live the BoM (Bureau of Meteorology) cannot "accurately" predict the upcoming daily tempreture and rainfall for the town that I'm in. They do very accurately predict the mean temp. and rainfall for the wider region. Doppler RADAR gives a very accurate measure of the amount of moisture held by rain bearing clouds, stable wrt broad area winds give a good path for that moisture's travel in the next 12-24 hours, experience + data give solid predictions for the amount of water to be shed, along with bulk cooling from shade and water fall + evaporation. The difficulty rarely lies in the bulk parameters for a broad area, the devil is in the small details which are inherently turbulent. To measure the accuracy of forecasting it first has to be ring fenced by what area you intend to predict the mean attributes for, the timescale you intend to project for, etc.
      - arlort 3y ago
        Yes, but all of that is unrelated to the original point The commenter I replied to was complaining about weather stations not using decimals. As you point out we can predict averages with a better accuracy, but services which have that accuracy do use decimals, where decimals aren't used is in consumer weather forecasts where an accuracy of less than 1 degree is anyway useless because > the devil is in the small details which are inherently turbulent
javawizard 3y ago
It gets even better: take that 1kg of water at 0°C, add 100 kilocalories of heat energy, and it's now 100°C and just about to boil. (That's assuming you're at sea level, as another commenter noted - if you're at 5,000 feet, the boiling point of water is something like 95°C.)
akira2501 3y ago
If you do this at Sea Level when Air Pressure is the barometric mean pressure with nothing but H2O, yes. Otherwise, not exactly, in ways that require formulas to quantify. Metrology is the dirtiest of all sciences, it does not grant simplicity. Anyways.. the counter example was the old definition of the Ampere: "the constant current which, if maintained in two straight parallel conductors of infinite length of negligible circular cross section and placed one metre apart in a vacuum, would produce between these conductors a force equal to 2 × 10−7 newton per metre of length." Perfectly unrealizable within this Universe.
tzs 3y ago
It has some warts. A mole of electrons has a charge of about 96487 coulombs. 100000 would have been nicer.

akira2501 3y ago

> the celcius was based off the freezing and boiling point of water at sea level These are not particularly great choices. Water transitions to a solid when it freezes, and distance from sea level has a massive impact on the boiling point of water which Celsius did promptly characterize. Also, somewhat weirdly, Celsius used to be inverted, with 100 being freezing and 0 being boiling.

IvyMike 3y ago

> The kilometer was based on 1/10000 the distance between the poles and the equator. The definition we should have used (and almost did) was that the meter was the length of a pendulum with 1 second swing (in other words, a pendulum with a 2 second period). https://maa.org/sites/default/files/images/upload_library/22/Schwartz.pdf https://maa.org/sites/default/files/images/upload_library/22... If we had done that, the gravitational constant of Earth would be exactly pi^2 m/s^2: Neat, right? https://godplaysdice.blogspot.com/2007/09/why-g-2.html https://godplaysdice.blogspot.com/2007/09/why-g-2.html

irrational 3y ago
I wish it had been defined in relation to the speed of light in a vacuum. 299,792,458 metres per second. Set it at 300,000,000 meters per second and derive the length of the meter from that.
- reaperman 3y ago
  > I wish it had been defined Wish what had been defined? the second?
  - ryanmcdonough 3y ago
    > and derive the length of the meter from that. I would assume they meant meter since they wrote that.
  - irrational 3y ago
    The meter. The distance light travels in a second in a vacuum is fixed. Divide that distance by 300,000,000. That is the length of 1 meter.
    - reaperman 3y ago
      So the current definition is: > The meter (m) is defined by taking the fixed numerical value of the speed of light in vacuum c to be 299,792,458 when expressed in the unit m s−1, where the second is defined in terms of ∆νCs.[0] Your proposed change is keeping this the exact same but changing 299,792,458 to 300,000,000? You said: “I wish it had been defined in relation to the speed of light in a vacuum.” I believe it is already, as written above. 0: https://www.nist.gov/pml/owm/si-units-length#:~:text=The%20meter%20(m)%20is%20defined,terms%20of%20∆νCs https://www.nist.gov/pml/owm/si-units-length#:~:text=The%20m....

qball 3y ago

>The kilometer was based on 1/10000 the distance between the poles and the equator. And that measurement they got was ultimately off, which is why the meter became (until its later redefinition), for all intents and purposes, "the length of some arbitrary metal bar". Clearly, "some fragment of roughly how large the Earth is" is a base unit designed first and foremost for human-scale measurements, and definitely not by self-fellating academics that would never seriously have to use the thing (and whose work does not, by and large, depend on the base unit used; Americans use thousandths-of-an-inch for everything under 1/64th). Fortunately, metric time was too weird even for the French. >but by measurements everyone on the planet could reproduce using the sun and a bit of water, at least to a very acceptable approximation. By contrast, the "foot", which is literally named after the device used to approximate it. The median human being has two of these. In fairness, you usually have to be taught which part of one's body approximates the inch and is thus harder to do. >join the metric system The metric system was initially imposed at gunpoint by the French upon most European nations in the first place due to the French going batshit insane just before 1800 and conquering most of the Continent. The Russians, being a nation that rather famously was not conquered by the French during that time, would retain Arshins until Communism (at which point the Soviets would impose the metric system, also at gunpoint- kind of sensing a theme here); the English would retain the Imperial system even longer than that. It's also why people living in the only nation that really has a choice all measure distance and height in (square) feet, inches, and kilometers (per hour), human weight in pounds (and very rarely ounces), most other weight in grams and kilograms, non-cooking-related volume in liters, and non-cooking-related temperature in celsius. It would have been objectively better from a usability to have just set '1 meter = 1 foot' and call it a day- could have even been (one of) the French foot, too. But no, just had to fuck it up for everyone who actually has to use it because "we know better".

mathieuh 3y ago
I never thought I would see an American Exceptionalist comment about a system of measurements. Metric measurements are as intuitive to me as American customary units are to you. I can just as easily use my handspan or the lengths of my fingers to estimate lengths in centimetres as you can in inches. I know without thinking what clothes I should wear when I see the weather forecast in Celsius. I know roughly what temperature I should set the oven to in Celsius based on what I’m cooking. Having grown up in a metric country, American or imperial units mean nothing to me. If I’d grown up in America I’m sure American units would be intuitive for me. The only difference, as you say, is metric is far easier and more intuitive as soon as you want to do anything complicated with those measurements.

tzs 3y ago

> The basis for the metric system was not defined by some arbitrary prototype at first, but by measurements everyone on the planet could reproduce using the sun and a bit of water, at least to a very acceptable approximation. I've got sun here and a well that will give me almost 50 liters/minute of water indefinitely. What measurements do I need to do to get a good approximation of the meter?

deleted 3y ago
[deleted]
eqvinox 3y ago
Problem is "the planet" is part of the requirements in that sentence too, since the original meter definition was 1/40000 of the circumference of the earth. You don't need to sail around the world for that, you can get it by shadow measurements, but you need measurements from two places on earth at the same time of year/position of the sun. cf. [ https://en.wikipedia.org/wiki/Eratosthenes#Measurement_of_Earth's_circumference https://en.wikipedia.org/wiki/Eratosthenes#Measurement_of_Ea... ]. The result you get from that is knowing what fraction of the earth's circumference is between the two places, which with the 1/40000 definition you can convert to meters. It's certainly doable, but you need the places to be reasonably far apart to get any accuracy, so… more of a "summer road trip" project, but could be fun with kids? ;) To be fair, the entire idea of metrology is that a few people do the work to get primary references and you distribute from there. There's a reason entities like NIST and PTB gets tax dollars.
- Valgrim 3y ago
  Kids? I would probably have the time of my life organizing an expedition with 5-6 full grown adults where the goal would be to go out there with nothing but our brains and hands, no device or ruler or anything like that, and figure out the length of a meter.