On the Fahrenheit scale, why is 32 freezing and 212 boiling?

[AG9Y]

I remember being told this by my science teacher, Mr. Rockwell, way back in high school. Mr. Fahrenheit needed a way to calibrate his thermometers. What he used was a glass of ice, and his body temperature. He would put the new thermometer in a glass of ice water. Where the mercury would settle he would mark as 32 degrees. Why, I will get to in a minute. He would then put the thermometer under his arm pit. This would give him his axial (I think that is the term) body temperature, which is a bit lower than taking it orally. He would mark this as 96 degrees. Why? Because there are 64 units between 32 and 96. I will wait while you do the math. Now to mark the rest of the units on the thermometer he only needed to measure the difference between his two marks and make a new mark halfway between. This would be 64 degrees. Dividing in half again he would have 48 and 80 degrees. He could keep dividing by two until he had the unit numbered from 32 to 96. He would then measure the distance between 32 and 64, then make a mark this distance below 32. That would be 0 degrees. Now he could again keep dividing the distance between 0 and 32 in half until he had a mark for each degree. The reason for 32 marks below freezing is that is as cold as he ever expected he would have to measure something.

So the real reason that water freezes at 32 degrees Fahrenheit, and axial body temperature is 96 degrees is so there are 64 divisions between them. Making marking the degrees in between much easier.

[bibliophage]

On the Fahrenheit scale, why is 32 freezing and 212 boiling? What do 0 and 100 mean? (http://www.straightdope.com/classics/a891215.html)

I remember reading long ago that Fahrenheit chose his zero point as the coldest temperature measured outside of where he worked in the year he was developing his scale, and 100º was the warmest it got. Years later I found climate data suggesting that it rarely gets as warm as 100º or as cold as 0º in whatever city it was that he was working in.

[AHunter3]

I thought it was the freezing and boiling point of whatever medium he originally used as his liquid. (It wasn't mercury; might have been an alcohol derivative--I can imagine an alcohol mix boiling at 100° F and freezing at 0° F, that sounds about right.

[Arnold Winkelried]

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[Ned]

I understood that 100 was set by the body temperature of his wife who had a bit of a high body temperature. The zero was ice mixed with equal parts salt.

Myth?

[Danielinthewolvesden]

100 was set as normal human body temp. 0 was the lowest temp he could get in the lab- using salted ice. He figured then there would be little need for "below zero" as temps would rarely get that low. And that 100 would be easy to remember, and get. Thus- since he, as the inventor, set the standards at 0 and 100- it is the other folks who are/were wrong at giving body temp as 98.6. However, since he also gave a few other marks, such as freezing or boiling of water, folks fixated on those as the "standards"- however- they are wrong. Incidentally, the centigrade/Celcius scale is no more "metric" than the Fahrenheit one- the French just picked that Cetigrade scale as the English used the F one.

That is also why they put the "meter" at 39", instead of a yard- to spite the English. One of the reasons why the metric system is not as useful as it could have been- is that so much of it was done to spite the English. The "english" foot/pound system, while mathematically wierd, had units that were useful in everyday life. A Meter is a bit too big. A gram is to small. They had to "back-engineer" the "hectare" and the "metric ton" to get some useful units to measure land & large wieghts, and a "square kilometer" is too big for everyday usage- and saying "a thousand kilograms" is a bit unwieldy.

[Kyberneticist]

Originally posted by Danielinthewolvesden

That is also why they put the "meter" at 39", instead of a yard- to spite the English.


Metre was picked in an attempt to have a standard unit based upon something measured frequently, the earth.
Here, I found a convenient page (one of many) explaining how it was created, and what the units are. You might find it useful...
http://www.hlalapansi.demon.co.uk/Metric/


One of the reasons why the metric system is not as useful as it could have been- is that so much of it was done to spite the English. The "english" foot/pound system, while mathematically wierd, had units that were useful in everyday life. A Meter is a bit too big.

Mathematically weird is precisely why the metric system was created. It is mathematically standard. It was not an anti-english plot. It would be simply impossible to stay close to all english measurements, since they varied too much.

A gram is to small. They had to "back-engineer" the "hectare" and the "metric ton" to get some useful units to measure land & large wieghts, and a "square kilometer" is too big for everyday usage- and saying "a thousand kilograms" is a bit unwieldy.

Personally, I think the system is quite elegant.
1 cubic centimetre of water at STP weighs one gramme. This makes a lot of rough calculations easy, given how much is water.
This same water marks 0 and 100 on the Celsius temperature scale. 1 degree is very very close to the triple point of water.
A litre is roughly a kilogramme of water.

If you don't like saying tonne or metric tonne, then use the original notation as it was intended. Say "megagram". There are units above 103 you know... Personally I use from deca,kilo,mega,giga,tera, and peta going up, and deci,centi,milli,micro, and nano going down. That's enough for comp. sci. (and the unit names have been slightly adapted :D ) although I suspect engineers and scientists on this board probably use stuff like femtoseconds fairly commonly.
Hectare I've never heard of. Is it 1/10th of a kilometer, a hectometer?
Metric isn't going to go away simply because it is flexible as well as standard. If we're going to have the "metric is unnatural debate" all over again, you're going to have to find a unit that can't be named easily. Yes, decimetre is more wordy then, say, a foot. But you're going to have to expect some wordiness in a standard system of measurement.

[Kyberneticist]

Er. My bad, should stick to the units I'm intimately familiar with.
The triple point of water is just a little over 0, .01 actually.
Faulty memories of chemistry class...

[bibliophage]

Originally posted by Kyberneticist

Hectare I've never heard of. Is it 1/10th of a kilometer, a hectometer?
A hectare is a unit of land measure, a little less than 2.5 acres. It is 100 ares and an are is 100 m2.

[Danielinthewolvesden]

Kber- I disagree- it is my opinion that they wanted a length measurement AROUND, but greater tha a yard- and found out you get get there by taking 1 millionth of the circumference of the earth, or whatever. Since there was no way to get any measurement of the earths circunference or diameter to within a mile or so- they were taking a guess anyway. They simply had no way to precisely measure it in those days. And " the earth" measured frequently? How many times have YOU gone out with a giant tape to measure the Earth?

True- they could not have stayed close to ALL the english measures- but not by coincidence- they did to several.

They could have simply made "meter=yard" and it would have been just as "scientific". Then a cc still could have equaled a gram, etc.

The problem was when they selected the "base"- the circumference of the earth- is a very silly base. It DOES change, and it was impossible to measure precisely. Note that now they use a std of a 15 place or so % of the speed of light. They COULD have selected something which was a round number.

A hectare is 10000 sq meters. However- there is no prefix for 10000. So- in order to have a usable measure of land area- they made one up.

[pldennison]

Originally posted by Danielinthewolvesden
Since there was no way to get any measurement of the earths circunference or diameter to within a mile or so- they were taking a guess anyway. They simply had no way to precisely measure it in those days. And " the earth" measured frequently? How many times have YOU gone out with a giant tape to measure the Earth?


What, are you kidding? Eratosthenes was able to measure the circumference to within a few hundred miles more than 2,000 years ago with little more than sticks and shadows. By the time the French were developing the metric system, the tools for measuring a portion of arc on a terrestrial meridian were, to say the least, somewhat more advanced.

The problem was when they selected the "base"- the circumference of the earth- is a very silly base. It DOES change, and it was impossible to measure precisely.

Nonsense. Scientists as far back as Newton knew that there was polar flattening taking place, and were working on calculating its severity (which amounts to around 1/300, or a difference of around 26 miles).

[RM Mentock]

Originally posted by Danielinthewolvesden
Kber- I disagree- it is my opinion that they wanted a length measurement AROUND, but greater tha a yard- and found out you get get there by taking 1 millionth of the circumference of the earth, or whatever.

Disagree with you both. One more, and we can get this moved to GD.

The meter was the length of the so-called "second" pendulum,
which took one second to swing from side to side. That is why the acceleration of gravity is so close to pi squared. (g=9.81 m/s^2, and pi^2=9.87)

However, they wanted a standard that was more, uh, rigid. The pendulum period changes with altitude and latitude, so they searched around until they discovered that 1/40000000 of the circumference of the earth would be very close. Plus, they could get government funding for a scientific expedition to measure it.

[John W. Kennedy]

A) Cecil's column gives the full Fahrenheit story. Why clutter up the board with urban myths?

B) The Metric System was developed by the French, who weren't bloody well using the English system in the first place!

C) _Which_ "foot/pound" system? The English foot? The American foot? (They weren't the same until both were adjusted to a compromise value, defined as exactly 0.3048 meters.) The English avoirdupois pound? The English Troy pound? The American avoirdupois pound? The American Troy pound? And which ton? The American ton of 2000 American avoirdupois pounds, or the English ton of 2240 English avoirdupois pounds? (Actually, I'm still oversimplifying the mess.)

Do you know what an "acre" actually is? It's an area of land one chain wide by one furlong long. How much is a furlong? 10 chains. What's a chain? 4 rods. What's a rod? 25 links. What's a link? 7.92 inches. (That's in America. The English system has an intermediate unit of "1 perch", which is 1/4 of an acre.)

By the way, the pound isn't a unit of mass (comparable to a kilogram). It's a unit of force (comparable to a newton). The "English" unit of mass is a "slug", roughly 15 kilograms. Or, if you like, you can use the "pound-mass", (something under half a kilogram), in which case you can use the "poundal" (a bit more than an ounce) as your unit of force.

Bleagh!

[Danielinthewolvesden]

Pld Yes- the Greeks could do it within a couple hundred MILES. The French could, AFAIK do it within 10 miles or so. Currently- the meter is based aupon the speed of light- measured down to TEN (10) significant figures. The French could not even get within an order of magnitude of that. Thus- they "base" they picked- could not, and still is not measured "precisely"- as ten sigfig is what they ask for.

John- what UL's?

[John W. Kennedy]

Cecil's original article goes into great and circumstantial detail about the origin of the Fahrenheit scale. So why jump in with a half-digested version of something remembered as having been retailed by a schoolteacher (a class rarely expert on anything except the watered-down and politically-correct dregs of psychology, sociology and anthropology taught s.v. "Education", and especially unlikely to be expert in cross-discipline fields like the history of science), as though Cecil had never bothered to answer the question in the first place?

[Danielinthewolvesden]

John- read the very first line- "researchers have gone to their grave trying to figure out what Fahrenheit was up to." Thus, how F actually came up with his numbers is not really known. My Upper div Physics prof actually did his PhD on temp scales- so i accept his reasoning. Not that cecil is wrong, per se- but there is a certain amount of guesswork involved.

[Chronos]

John, does that English ton predate the metric system? It looks to me like somebody's trying to match a metric ton, but with numbers that come out reasonably close to round in the avoirdupois system.

As for the precision of the measurement of the Earth, how precisely is the length of the King of England's arm measured? I'd say that the French had the advantage on that one.

[John W. Kennedy]

A) The "King of England's arm" story -- which I don't offhand remember the truth of -- was only how the single national standard yard was set, by one particular measurement of one particular king on one particular day. (Previously, every town had had a standard yard, pound, etc.,.) The Metric system in this regard is no better or worse; the practical standards by then were metal bars for all systems, and, after a few decades based on wavelengths of specific spectral emission lines (the orange line of Krypton 86 is the one I remember), the standard is now based on the speed of light. But it's always been a question of using a standard that is precisely measured and precisely copied, using available instruments and tools.

Using the size of the Earth to set the standard was just a reflection of period thinking, the same that established a ten-day week and attempted to establish a ten-hour day. Down with everything older than us! was the cry; those of us in our late 40's and early 50's will recall something along the same lines.

That the Metric System came out better than the rest is largely an historic accident. Decimal scaling helps, but I suspect the real reason is that it was an effective international standard in the days when many countries still didn't have decent national standards; this led to its universal adoption by scientists.

B) The traditional ton antedates the Metric System. The rough equivalence of the various tons and the tonne is a coincidence.

[AG9Y]

This is straight from Cecil's answer on the subject of why freezing in 32 and body temperature 96.

"Then, for reasons nobody has ever been able to fathom, he multiplied all the numbers by 16/15, making 32 freezing and 96 body temperature. Boiling point for the time being he ignored altogether."

So Cecil is saying, he does not know why 32 was picked as the freezing temperature and 96 for body temperature. I'm only passing on information I heard which makes a lot of sense. (At least to me.) If you are going to make a scale, it is nice to have everything in powers of two. (64 degrees between freezing and body temperature. 32 between 0 and freezing.) Then to mark off individual degrees, you just keep dividing the distance between your marks by half until you get the accuracy you desire.

Go back to the figures of 30 and 90 which Cecil mentions. (These are the figures multiplied by 16/15 referred to above.) Half way between them would be 60 degrees. So far so good. Half way between 30 and 60 would be 45 degrees. Again so far so good. But, halfway between 45 and 30 would be 37.5 degrees. And each half from here on out makes it even worse. Of couse, Fahrenheit could have measured the distance between 45 and 30 on his scale and figured out what 1/15 of it would be, then mark individual degrees that way. But what a pain!

It works a lot easier using my system. Halfway between 32 and 96 is 64 degrees. Halfway between 32 and 64 would be 48 degrees. Halfway between 32 and 48 would be 40 degrees. Halfway between 32 and 40 would be 36 degrees. Halfway between 32 and 36 would be 34 degrees. And finally, halfway between 32 and 34 would be 33 degrees. By starting with 32 and 96 you can mark all the way down to individual degrees without doing anything more than measuring the distance between two points on your thermometer and dividing that length in half. Heck, you can even continue on and mark 1/2 degrees, 1/4 degrees etc, if you wanted to.

Seems a simple and easy way to mark his thermometer to me.

And finally, can anyone else come up with a reason to use 32 for freezing besides the convenience of it being 2 to the fifth power?

[Alphagene]

Here (http://physics.nist.gov/cuu/Units/meter.html) is a good history of the standardization of the meter. I found this quote:

"However, the first prototype was short by 0.2 millimeters because researchers miscalculated the flattening of the earth due to its rotation."

This suggests two things: 1) That the French were aware of the flattening of the earth, they just didn't get the amount exactly right. 2) Their calculation of "one ten-millionth of the length of the meridian through Paris from pole to the equator" was only off by (correct me if I'm wrong) 0.02%. If that's just a "guess" then it's a pretty damn good one.

Also as for the metric system not being "as useful as it could have been", I disagree completely. The utility of the metric system is vasty superior to the English system not because of the accuracy of the intended base units, but because of its flexiblity. Is there an efficient way to describe the diameter and mass of a single hydrogen atom using English units? I'd love to hear it if there is.

Additionally, I have seen no indication that the French instituted the SI to spite the English, even in part.

You really should provide some cites to back up your claims, Dan.

[Bryan Ekers]

It's true that Celsius isn't any more 'metric' than Farenheit, but the rest of the metric-bashing struck me as strange. A system survives becuase:

a- it's useful, and
b- nobody cares enough to make the effort to change it.

The U.S. can happily keep using "imperial" measurements forever becuase they have such a huge amount invested in it. Besides, most of the obscure measurements that anti-imperial types (rebel forces?) hold up as examples that the whole system should be junked have fallen out of use anyway. If a person is satisfied with inches, feet, yards and miles, why smugly bash them over the head with chains, furlongs and rods, unless they're into that sort of thing?

I'm Canadian of a certain age, so it turned out my textbooks were imperial up to Grade 3 and then changed over, along with the rest of the country, in the late seventies. As a result, I'm a happy hybrid, using whatever measurement suits the application at hand. I judge large distances and speeds in kilometers and kilometers per hour, becuase I'm usually measuring them on maps and using my car's speedometer, marked in kilometers. I measure smaller distances, as in the width of a room, in feet and inches, becuase that's what most of my measuring tapes use. Volume is in litres, because the products I buy are measured as such and I have no patience for ounces, pints and quarts anyway. The food I buy is measured by weight in grams or kilograms, but if I pick up a piece of non-edible equipment, I'm more likely to say "damn, this must weigh 70 pounds!" instead of 30 kilograms. As for the rare times I must consider areas large enough to be uncomfortable in square feet, hectares are just fine, becuase I can never remember what the hell an acre is, anyway.

So lighten up, already, be it in pounds or kilos.

[freightliner]

I think the following is interesting about the metric system. The meter is defined as "The distance travelled by light in vacuum during a time interval of 1/299 792 458 of a second".

The second is defined as "The duration of 9 192 631 770 periods of radiation corresponding to the transition between the two hyperfine levels of the ground state of the cesium-133 atom".

And the kilogram is defined as "The mass of the international prototype kilogram" (I think this is the platinum-iridium deal they keep in France somewhere).

So:
(A) the kilogram definition seems a lot more arbitrary than the other two. I think a mass standard should be based on something like the mass of Carbon 12 atom.

(B) A lot of the weirdness in the definitions of meter and second are probably because of a desire to keep to the "standard" second that people had been using for a long time (i.e. 1/86400 of a day). But how did they ever know to set the second as 9192631770 perods of radiation, and not, say, 9192631780 periods.

(C) My car gets fourty rods to the hogshead and that's the way I like it!

[John W. Kennedy]

The U.S. can happily keep using "imperial" measurements forever becuase they have such a huge amount invested in it.


No we don't. We never used the Imperial system, which differs from the US system in almost every respect.


The kilogram definition seems a lot more arbitrary than the other two. I think a mass standard should be based on something like the mass of Carbon 12 atom.


Arbitrariness is less important than exactness. If we can ever count the atoms in 12 grams of pure carbon-12 more accurately than we can weigh the Standard Kilogram in Paris, we'll do that, but right now it's impossible.


A lot of the weirdness in the definitions of meter and second are probably because of a desire to keep to the "standard" second that people had been using for a long time (i.e. 1/86400 of a day). But how did they ever know to set the second as 9192631770 perods of radiation, and not, say, 9192631780 periods.


The original definition was 1/86400 of a day. Then it was, if I recall correctly, 1/31536000 of the tropical (i.e., not siderial) year 1900. It probably went through some more variations before reaching the current value. Essentially, every time that a measurement is found that is more generally reproducible and more exact than the current standard, the standard is likely to change.

[Bryan Ekers]

Originally posted by Bryan Ekers
The U.S. can happily keep using "imperial" measurements forever becuase they have such a huge amount invested in it.


Originally posted by John W. Kennedy
No we don't. We never used the Imperial system, which differs from the US system in almost every respect.



Well, excuse ME, but the reason the word "imperial" was originally in quotes shows that I am aware that various definitions exist, though I didn't feel compelled to list them. Any system (or language, or religion) that is old enough is going to have local variations.

Besides, if you want to get nitpicky, what do you mean by 'almost every respect' ? Are inches, feet, gallons and miles entirely different in England than in the U.S.? Maybe they only sound different because of that snooty accent.

"Imperial" in the sense I used it can casually refer to the system of familiar non-metric units including pounds, feet, and gallons without delving into local variations. If anything, that provides a stronger argument for going metric, since metric units are more rigidly and internationally defined.

As for the investment angle I was going for, it's merely a restatement of part of a Cecil column (Whatever happened to adoption of the metric system in the U.S.?, 02-Jun-95) which I quote forthwith:

[B]
Converting to metric will cost money, the critics say, and unless you're involved in foreign trade it confers no benefit.

These arguments are specious. If people still calculate horse races in furlongs, a medieval measure, there's nothing to prevent them from using feet and yards in sports indefinitely (although the Olympics have gotten people used to meters). And while converting to metric costs something, much of the money has already been spent. Rare is the auto mechanic, for example, who doesn't have metric wrenches.


The point being that Americans can cling to non-metric measurements for as long as they want, and that there would be a cost to forcing the metric issue on the entire country if there is no compelling need to do so, though individuals who felt an advantage to going metric (i.e. Olympic athletes, auto mechanics) have already done so.

"But she'll get 40 hectares on a single tank of kerosene."
-Crazy Vaclaz

[John W. Kennedy]

Virtually all the US and Imperial units are different. I'm amazed that you, a Canadian, don't know that an Imperial Gallon is about 120% of a US Gallon.

The US Inch and the Imperial Inch were replaced by the International Inch in 1959, so they're equal now, but before 1959, they were not.

Don't say "Imperial" if you don't mean it. The correct term for "the mess the UK and US used to have in common (but only approximately), which now only the US uses" is "English".

[freightliner]

Arbitrariness is less important than exactness. If we can ever count the atoms in 12 grams of pure carbon-12 more accurately than we can weigh the Standard Kilogram in Paris, we'll do that, but right now it's impossible.


The limiting factor with counting the atoms in a given mass would be the precision to which we know Avogadro's number, which we know to about 0.59 parts per million. I would be surprised if anyone can measure the mass of the kilogram standard any more accurately than that. So really, the difficulty would be precisely measuring out 12 grams (or 1 kilo) of Carbon 12, as opposed to determining the number of atoms therein. No matter what the standard is, there is always the practical limitation of how well we can measure mass on a macroscopic scale.

This makes me wonder... what is the standard way to measure the mass of this standard? Considering that Newton's gravitational constant ("big G") is only known to 128ppm precision, any method of "weighing" the kilogram standard based on the effect of Earth's gravity should be limited to this precision, right? Isn't mass generally inferred from some measurement of a force, or a force balance? It's not trivial to measure any force, or any acceleration due to a force, to great precision.

Anyway, the reason I think the kilo (or the gram) is inconvenient is because a gram-mole turns out to be 6.022e23 molecules. If we could chose, for example, 1 MU-mole = 10.000^24 molecules, and then our macroscopic mass unit could be the "MU" (roughly 1.66 kilos), it would be easier to do convert from mass to number of molecules in your head. In keeping with the whole factor-of-10 theme of the metric system.


The original definition was 1/86400 of a day. Then it was, if I recall correctly, 1/31536000 of the tropical (i.e., not siderial) year 1900. It probably went through some more variations before reaching the current value. Essentially, every time that a measurement is found that is more generally reproducible and more exact than the current standard, the standard is likely to change.


What I was really trying to point out here is that there is a discrepancy in the precision of the measurements. According to the above, the original "second" was known to about 5 significant digits (assuming those zeroes in 1/31536000 aren't all significant). Then, when the cesium atom standard was chosen, they defined that to 10 significant digits. My question is, how did they know what to define as the last 4 or 5 digits when the original standard that they were trying to match wasn't known to that precision. I think they could have just as easily chosen 9 192 632 000 periods of radiation (with two of those three zeroes being significant), and matched the previous standard just as well as they do now.

It kind of reminds me of when some of my students submitted a design project and "estimated" the annual profit to be $35,267,891.05, based on 90,000 tons per year and 55 cents per pound of product, minus raw materials and capital.

[Bryan Ekers]

Originally posted by John W. Kennedy
Virtually all the US and Imperial units are different. I'm amazed that you, a Canadian, don't know that an Imperial Gallon is about 120% of a US Gallon.

The US Inch and the Imperial Inch were replaced by the International Inch in 1959, so they're equal now, but before 1959, they were not.

Don't say "Imperial" if you don't mean it. The correct term for "the mess the UK and US used to have in common (but only approximately), which now only the US uses" is "English".

Sigh. This is the kind of nitpicking that can only strangle discussions, since each participant has to sprinkle asterisks and footnotes throughout their statements. Not having been alive in 1959, I'm cheerfully prepared to ignore the standardization battles of that era, although I do remember reading, of all things, an Encyclopedia Brown mystery story in which the solution hinged on five quarts equalling a gallon in Canada (and presumably the UK and other "imperial" places, as well). I was suitably confused by this at the time and now I happily embrace litres, which at least aren't subject to local interpretation.

Anyhoo, I'll continue to use the phrase "imperial" to mean "non-metric" becuase it's ultimately less confusing. The system that "now only the US uses" is called "English"?
Riiiight. So what do the English use? Consarn it, the next time an empire collapses, we really have to clean up these loose ends better.

The exact quantities involved were never relevant, anyway. I was discussing which system is useful for a given situation and the natural resistance to change it, once selected. If you don't like it, then don't buy any gasoline at my chain of "BryCo" filling stations.

[John W. Kennedy]

The limiting factor with counting the atoms in a given mass would be the precision to which we know Avogadro's number, which we know to about 0.59 parts per million. I would be surprised if anyone can measure the mass of the kilogram standard any more accurately than that.


1 in 10^9.


This makes me wonder... what is the standard way to measure the mass of this standard? Considering that Newton's gravitational constant ("big G") is only known to 128ppm precision, any method of "weighing" the kilogram standard based on the effect of Earth's gravity should be limited to this precision, right? Isn't mass generally inferred from some measurement of a force, or a force balance? It's not trivial to measure any force, or any acceleration due to a force, to great precision.


Vacuum balance, with transposition from one pan to another and other checks. A balance is not dependent on local G.

The measurement people are very aware that use of a physical prototype is unsatisfactory, and they'd be very happy to replace it, but, so far, it hasn't been practical.

Anyway, the reason I think the kilo (or the gram) is inconvenient is because a gram-mole turns out to be 6.022e23 molecules. If we could chose, for example, 1 MU-mole = 10.000^24 molecules, and then our macroscopic mass unit could be the "MU" (roughly 1.66 kilos), it would be easier to do convert from mass to number of molecules in your head. In keeping with the whole factor-of-10 theme of the metric system.


Yes, and it would be even nicer to use a system based on Planck's constant, the speed of light, the rest mass of an electron, the electron charge, and Boltzman's constant. But it ain't gonna happen.


According to the above, the original "second" was known to about 5 significant digits (assuming those zeroes in 1/31536000 aren't all significant).


They were meant to be significant. It's just 365*24*60*60.


Then, when the cesium atom standard was chosen, they defined that to 10 significant digits.


They obviously couldn't carry the year 1900 around with them to calibrate with. The _real_ standard was one or more high-precision clocks. Each new standard reproduces, as well as possible, the previous standard, warts and all. (Remember, the higher-precision technology will have been in place for a while, before being adopted as a standard.)

Anyhoo, I'll continue to use the phrase "imperial" to mean "non-metric" becuase it's ultimately less confusing. The system that "now only the US uses" is called "English"?


"English" is the correct term for "the whole foot/pound/gallon mess". "US" is the correct term for the standard form of the English system that is still used in the USA. "Imperial" is the correct term for the now obsolete standard form of the English system that was developed in the Victorian era for use throughout the British Empire.

It is not "less confusing" to call all apes "gorillas", it is not "less confusing" to call all Jews "Hassidic", and it is damn well not "less confusing" to call all English measures "Imperial". The US never used the Imperial system, which did not even exist at the time of the Revolution.

[Bryan Ekers]

Originally posted by John W. Kennedy
[quote]
It is not "less confusing" to call all apes "gorillas", it is not "less confusing" to call all Jews "Hassidic", and it is damn well not "less confusing" to call all English measures "Imperial". The US never used the Imperial system, which did not even exist at the time of the Revolution.

Well, when the National Association for the Advancement of non-Metric Measurements or the Foot-Pound-Gallon Anti-Defamation League shows up at my door to demand an apology, I'll consider it. For now, I'll just keep using my generalizations, especially when they have no relevance to the larger subject. Does it really matter if an American and an Englishman disagree about the exact quantity of a "gallon"? The point was how comfortable they are in continuing to use a non-metric measurement, despite the changeover in most of the rest of the world.

If you want to keep using gallons, be my guest. I won't even bug you on how many mols in each one.

[John W. Kennedy]

I find that, in fact, finding a new definition for the kilogram is an official ongoing project of the BIPM (International Bureau of Weights and Measures).

[BillK]

Can't make an obvious error and get past an engineer! Before I Quote the true answer, think about our Northern highways for a minute. Why would salt be of any use on icey roads if it only bought 12 degrees of margin? A lot of work and a lot of salt wasted while still at a balmy 18 degrees - NOT!
I remebered what some of the posts have mentioned - that zero degrees is the lowest ice/salt temperature. But here is a quote from a website called "Numericana.com":


In 1714, when G.D. Fahrenheit devised the temperature scale now named after him, he meant 100° to be the normal temperature of the human body.

On the other hand, he (first) defined 0° as the lowest temperature he could achieve in the laboratory by using salt to melt ice. (Although it's, in fact, possible to go a few degrees lower by doing the same experiment under ideal conditions.) This same temperature was also then a record low for Danzig (in 1709).

These two points, however, were later judged to be far too imprecise a basis for a temperature scale. Instead, it was decided that the ice point would be exactly 32°F and the steam point 212°F.

In this redefined Fahrenheit scale, the normal temperature of the human body is around 98.6°F (which is exactly 37°C, by the way).

The latest precise definitions of both the Farhenheit and the Celsius scales no longer refer to the ice point and the steam point. Instead, both definitions refer to the Kelvin scale of thermodynamic temperature (itself defined by stating that 273.16 K is the temperature of the triple point of water): The temperature of 273.15 K (just 0.01 K below the triple point of water) is equal, by definition, to both 0°C and 32°F, whereas 373.15 K is equal to both 100°C and 212°F. Of course, the new definitions match the old ones, except when the utmost in precision is called for...

[xejkh]

The gram was defined in an era where science was considered to be the best method available to do things -- witness how the scientists tried to base the metre on the earth's circumference.

The gram is defined as the mass of 1 cubic centimetre of water at its maximum density at 4°C.

Of course, the mass of 1 g is too small to be practical, so the base unit for mass was upgraded to the kilogram instead.

Instead of maintaining 1 cubic centimetre (or 1000 cc) of water at 4°C, scientists have now defined (in practice, though not in theory) that 1 kg is the mass of that piece of metal somewhere in France.

[angilion]

Originally posted by Bryan Ekers
Anyhoo, I'll continue to use the phrase "imperial" to mean "non-metric" becuase it's ultimately less confusing. The system that "now only the US uses" is called "English"?
Riiiight. So what do the English use?

Bits of each system, essentially, although there is a great deal of force being applied to require everyone to use SI units for everything. It is, for example, now illegal to sell items measured in the traditional English units, such as pounds and pints. Except that it isn't, sometimes, in some circumstances. Lots of fun to be had with that law.

In general usage, IME, most English people, along with most other British people, mostly use the traditional British units in most cases. Distances are in inches, feet or miles, weights are in pounds, though larger weights may well in in tonnes. Weights for a person, however, are in stones and pounds, where one stone is 14 pounds. A person's height is in feet and inches, not just inches. Liquids are measured in (milli)litres, except for drinks such as beer, which are measured in pints. Petrol is often measured in gallons as well as in litres.

Essentially, there is a lot of pressure to bring Britain into line with what will become the United States of Europe. While a country can have their own standards of measurement, a state can't. Most British people cheerfully ignore it and continue to use British units, but SI units will gradually become the norm, forced along by Europe. Personally, I'm familiar with either system. Younger people are more likely to use SI units, because that is what they will have been taught to use in schools. Anachronisms will no doubt survive for some while, such as beer being sold in pints.

[Chronos]

The gram was defined in an era where science was considered to be the best method available to do thingsCould someone please explain this sentence to me? The people defining the gram are scientists, who of course think science is the best method for doing things. And there is only one definition of the kilogram, based on the Standard Kilogram in Paris. The gram is not defined in terms of the density of water. It was once, but not currently.

[Irishman]

Sorry, Chronos, but to make that make sense, I have to assume I know what he's talking about and restate the point completely differently. And then I'm only sure that I think I know what I think he might have meant. ;)

He seems to be talking about defining the units of measurement on physical properties. Thus the kilometer was defined based on the circumference of Earth. And therefore the origin of the gram was based on an amount of water at a specified state (temp and pressure). But it was an impractical measure, so they use the physical kilogram mass.

I think he just mangled the use of the word science.

[SlowMindThinking]

The definition of all of the SI units, and more unit conversions than any of us care to see, can be found at:
http://physics.nist.gov/cuu/Constants/

Of course, these definitions are given by those who think that science is the best way to do things. Or, at least, the best way to do physics.