Kelvin had previously proposed to define an absolute scale of temperature independent of the properties of any particular substance in terms of Carnot's function by making F'(t) constant.
With Regard To The Scale Of Temperature, There Is Very General Agreement That The Absolute Scale As Realized By The Hydrogen Or Helium Thermometer Should Be Adopted As The Ultimate Standard Of Reference.
This unit is taken as being 4.180 joules per gramme-degree-centigrade on the scale of the platinum thermometer, corrected to the absolute scale as explained in the article Thermometry, Which Has Been Shown To Be Practically Equivalent To The Hydrogen Scale.