Not to be dense here but did you actually mean to say "I still don't understand why we don't use the word Celsius"?

I'm an American, remember?

Remember, centigrade refers to something observable and applicable. Celsius, like Fahrenheit and even Kelvin, is someone's name.

Or maybe there's my answer: In science, naming it after someone is the important thing. (Which I always thought was a joke in children's literature, television, and cinema.)

Remember, centigrade refers to something observable and applicable. Celsius, like Fahrenheit and even Kelvin, is someone's name.
Unfortunately, what it refers to is so counter-intuitive as to cause more harm than good.

Zero Centigrade is the boiling point of water.
One hundred Centigrade is the freezing point of water.
(Yes, read that again. No, I didn't get it wrong.)

"When Anders Celsius created his original scale in 1742 he inexplicably chose 0° for the boiling point and 100° for the freezing point."
https://www.brannan.co.uk/celsius-c...is the old fashioned,° for the freezing point.

Zero Centigrade is the boiling point of water.
One hundred Centigrade is the freezing point of water.
(Yes, read that again. No, I didn't get it wrong.)

Which is why all thermometers with °C still do the same thing. Oh, they don't. Maybe we all went to terrible schools, and that's why we can't do centigrade properly. Maybe I can find one of those old thermometers, perhaps from before World War I. None of my teachers knew, and the oldest was born during or maybe right before the war.

Indeed, I actually never had any idea there was some dispute about what direction the numbers should run. Thank you.

And, with centigrade being such a bad idea, what's with fixing it and then naming it after the guy who got it wrong?

Still, though ... I mean, since I'm riffing, what was Kelvin's deal? I mean, sure, we name science after people instead of function. LIke when my doctor uses his lannecusanus to listen to my heartbeat. Like the story about the guy who tried to call it a stethoscope, once upon a time, and was expelled from the Association for heresy. But if you're Kelvin, why use Celsius?

Okay, I'll stop now.

Or if you're Bob Seger do you know that you're not Kenny Rogers?

It's okay; you can leave your hat on.

Which is why all thermometers with °C still do the same thing. Oh, they don't. Maybe we all went to terrible schools, and that's why we can't do centigrade properly. Maybe I can find one of those old thermometers, perhaps from before World War I. None of my teachers knew, and the oldest was born during or maybe right before the war.

Indeed, I actually never had any idea there was some dispute about what direction the numbers should run. Thank you.

And, with centigrade being such a bad idea, what's with fixing it and then naming it after the guy who got it wrong?

Still, though ... I mean, since I'm riffing, what was Kelvin's deal? I mean, sure, we name science after people instead of function. LIke when my doctor uses his lannecusanus to listen to my heartbeat. Like the story about the guy who tried to call it a stethoscope, once upon a time, and was expelled from the Association for heresy. But if you're Kelvin, why use Celsius?

Okay, I'll stop now.
Kelvin's deal is that the scale named after him is far more useful for physics and chemistry, as it is directly proportional to the mean kinetic energy of molecules at a given temperature*, which manifests itself in a huge range of physical phenomena. So it is a fundamental temperature scale. Celsius and Fahrenheit, by contrast, are arbitrarily related to the freezing and boiling of one common substance, in Fahrenheit's case made even more arbitrary by inclusion of salt. This was done for practical reason at the time to provide a ready means of calibrating thermometers.

* The kinetic energy per atom, in a monatomic gas, i.e. with only 3 translational degrees of freedom, is 3/2 kT, where k is Boltzmann's constant and T is the temperature in Kelvin. For a diatomic gas the kinetic energy per molecule becomes 5/2 kT, once the temperature is high enough for the 2 rotational degrees of freedom to become excited as well (The 3rd rotation would be spinning along the molecular axis, which would effectively correspond to an electronic excitation, which would not become active until above the dissociation temperature for the molecule.)

So there: a little counter-riff from me on chemistry.

For completeness, just a quick note. The Kelvin scale is not completely "fundamental", in that the "distance " between numbers on the scale is an arbitrary choice. Specifically, the choice that was made is that a one-degree difference in Celcius is the same as a difference of one Kelvin in temperature; i.e. the "size" of a Kelvin is chosen arbitrarily to be the same as the "size" of a Celcius degree (which was originally based on the difference between the melting and boiling temperatures of water at "standard atmospheric pressure" (which is, itself, another approximately arbitrary choice)).

Nevertheless, the Kelvin scale is "more fundamental" than the Celcius scale, since its "absolute zero" is really an absolute - it corresponds to a universal physical property. In comparison, "absolute zero" corresponds to -273.15 degrees Celcius (or is it -273.16? I always forget.)

Farentheit's "zero degrees" was chosen based on the coldest temperature he personally could achieve in the lab with a modicum of effort. His 100 degrees was originally chosen as human body temperature - not quite right, as it turned out.

So, on a scale of relative arbitariness, Farenheit wins the prize for most arbitrary (of the scales still in widespread use*), followed by Celcius, then Kelvin. We can't actually do better than Kelvin, because any choice of the "size" of a degree is always going to be arbitrary. But that's true of all physical units that are not dimensionless. Miles and metres are arbitrary. Seconds are arbitrary. Kilograms are arbitrary; pounds are even more arbitrary.

In fact, the only really significant constants in science are the dimensionless ones. Their values are what they are, and we don't get to choose anything about them; nature decides. To understand this is actually to understand something important about science.

For completeness, just a quick note. The Kelvin scale is not completely "fundamental", in that the "distance " between numbers on the scale is an arbitrary choice. Specifically, the choice that was made is that a one-degree difference in Celcius is the same as a difference of one Kelvin in temperature; i.e. the "size" of a Kelvin is chosen arbitrarily to be the same as the "size" of a Celcius degree (which was originally based on the difference between the melting and boiling temperatures of water at "standard atmospheric pressure" (which is, itself, another approximately arbitrary choice)).

Nevertheless, the Kelvin scale is "more fundamental" than the Celcius scale, since its "absolute zero" is really an absolute - it corresponds to a universal physical property. In comparison, "absolute zero" corresponds to -273.15 degrees Celcius (or is it -273.16? I always forget.)

Farentheit's "zero degrees" was chosen based on the coldest temperature he personally could achieve in the lab with a modicum of effort. His 100 degrees was originally chosen as human body temperature - not quite right, as it turned out.

So, on a scale of relative arbitariness, Farenheit wins the prize for most arbitrary (of the scales still in widespread use*), followed by Celcius, then Kelvin. We can't actually do better than Kelvin, because any choice of the "size" of a degree is always going to be arbitrary. But that's true of all physical units that are not dimensionless. Miles and metres are arbitrary. Seconds are arbitrary. Kilograms are arbitrary; pounds are even more arbitrary.

In fact, the only really significant constants in science are the dimensionless ones. Their values are what they are, and we don't get to choose anything about them; nature decides. To understand this is actually to understand something important about science.
.....................And, just for really complete completeness, "Celcius" should be spelt Celsius.

.....................And, just for really complete completeness, "Celcius" should be spelt Celsius.
Oops. Thanks.

Happy new year, Sci-Forums!

Here’s to another year of learning, bickering, ad homs, woo, UFO sightings, debunkery, oh…and science discussions.

If you had two of the exact same thing, what would you do with the one most like the other one?

If you had two of the exact same thing, what would you do with the one most like the other one?

There is not one most like the other

But what if there were!

If you had two of the exact same thing, what would you do with the one most like the other one?
But what if there were!
The word exact rules that option out

I'm not a U.S. citizen, I'm Canadian.

Yet, I am pro U.S.

I believe a Japanese General in WWII remarked they were screwed when he saw the American armada.