## Tuesday, June 14, 2016

### Veritasium reminds us: Celsius Didn't Invent Celsius

I'm nearly always a sucker for a good tale of physics history. Especially those regarding the settling of temperature scales. A new offering from Veritasium's Derek Muller details the birth of the Celsius scale.

Celsius Didn't Invent Celsius

For my own part, I do something of dubious merit when teaching about temperature scales. To answer the question of why we have "degrees" when discussing temperatures, I tell a tale which may mix fact and fiction:
Fahrenheit used a salt and ice mixture to establish a zero point. He then used his own body temperature to establish 96. Why 96? Because it has so many factors, and that helps in dividing the scale into usable increments. Halfway between 0 and 96 is 48, half of which is 24, half of which is 12, half of which is 6, half of which is 3. If you start with 100, things get ugly after two halvings.
Fahrenheit discovered that the freezing point of water was 32 and the boiling point of water was in the neighborhood of 212. He decided to nail down those two points: 32 and 212 for the freezing and boiling of water, and dispensed with the salt-ice/body temperature standards. This moved body temperature closer to 99.
And therein lies lies the tale of degrees. Freezing and boiling can be interpreted as opposite processes for water. In one, liquid turns to solid; in the other, liquid turns to gas. Opposite processes. The difference between 32 and 212 is ... 180. Why not 180 degrees between opposite processes. It's geometrically perfect.
That's my story, and no one's talked me out of it yet. But I'm open to being brutally corrected.