I know that temperature can be found as a quantity proportional to some quantity which increases monotonically with "hotness". And we can use various methods such as mercury column, gas thermometer and resistors to do so.
And by calibrating all of this to the different phase transistion states of water, we can get a uniform temperature scale.
Now my question is what method was used for defining temperature on kelvin scale? I've heard that it's based on energy of gases but how would you measure "energy" of a gas?
I have read the accepted answer to this question:
And he says kelvin used thermometers different fluids but what kinds and how? Also I see a rankine absolute thermometer scale. What is this?
