| I'm not sure about the change of boiling/freezing point under different pressures, but I would hardly call Water an arbitrary substance. Also, for scientific use Kelvin is more applicable (I think?), but I see no problem with it in every day use. If it's below zero, it's freezing. If it's above 30 for 5 consecutive days, it's a heat wave. And it's used without decimals in any weather report I've ever seen across Europe. It really doesn't make much of a difference whether it's 24 or 25 degrees, let alone whether it's 24. 4 or 24.8. |