Gene Mechtly wrote in USMA 18483:
>On Thu, 28 Feb 2002, Stephen Davis asked:
>
>> ... why Centigrade was replaced by Celsius!!
>
>Steve,
>
>The kelvin scale of temperature is *defined* by fixing a *single*
>reference temperature, the "triple point" temperature of pure water,
>at exactly 273.16 kelvin. (where "triple point" means the temperature
>of ice, water, and water vapor in equilibrium)
>
>
>The zero on the Celsius scale is fixed at the "triple point" of water;
>at 273.16 kelvin.
>
>On the other hand, the zero on the centigrade scale had been set at
>the "ice point" of water, at 273.15 kelvin. (the temperature of melting
>ice)
>
>Although the difference is only 0.01 kelvin, the "triple point" is more
>accurately realized in laboratories than the "ice point", and therefore
>the Celsius scale is preferable to the centigrade scale.
>
>See Resolution 3 of the 9th CGPM of 1948, Page 122 in the BIPM Booklet.
>
>Gene.
The 9th CGPM in 1949 refined the definition of the centigrade scale in
Resolution 3, CR 63, as Gene has mentioned. Then in CR 64 the CGPM
resolved:
"From the three names ("degree centigrade", "centesimal degree", "degree
Celsius") proposed to denote the degree of temperature, the CIPM has chosen
"degree Celsius" (PV, 21, 88).
"This name is also adopted by the 9th CPGM (CR, 64)."
>From this it is apparent that there no difference whatsoever, except in
name, between the centigrade scale and the Celsius scale. I first met the
name "Celsius" in Germany in 1935. The principal reason for the change was
the existence of the angular scale that divided the right angle into 100
grades.
Joseph B.Reid
17 Glebe Road West
Toronto M5P 1C8 TEL. 416-486-6071
