Body heat is lost the fastest from the extremities. Which is the law that is based on this phenomenon?

Mammals from colder climates generally have shorter ears and limbs to minimise heat loss. This is called the Allen’s Rule. Animals surviving in the cold regions have shorter ears and tails, also called extremities. It is because of the fact that more surface area will increase the heat loss. By reducing the size of limbs, ear and extremities, they decrease the surface area to volume ratio.