Re: Temperature Scales

[David Bowman <David_Bowman@GEORGETOWNCOLLEGE.EDU>]

Regarding:

> Oops!  This is NOT the definition of the Celsius (note spelling) scale!!!
>
> Jim Green
>
> At 12:38 16 11 2000 , you wrote:
> > The Celcius temperature scale is based on the freezing and boiling points of
> > water. The temperature range was divided up into 100 degrees. Does anyone
> > know how the Fahrenheit scale was determined?
> > -tony

Jim is correct here.  The Celsius scale is based on the Kelvin
thermodynamic (absolute) temperature scale.  The temperature in degrees
Celsius of an object is *by definition* its thermodynamic temperature in
kelvins minus 273.15 (exact).

The Kelvin scale is calibrated at a single point such that the
thermodynamic temperature of 273.16 K (exact) corresponds to the triple
point of pure water (whose isotopic composition matches the terrestrial
averages).

As I recall, the melting point of pure water under 1 atmosphere of
pressure (i.e. 101325 Pa exact) is very close to 273.1525 K, and this
corresponds to 0.0025 deg C.

It was the old centigrade scale (not the current Celsius scale) that was
calibrated at the freezing and boiling points of pure water (at 1 atm)
to be 0 deg and 100 deg respectively.

David Bowman
David_Bowman@georgetowncollege.edu