In LY 201, a scientist named Hans completed his experiments leading to the development of the thermometer, in which the metal mercury (in its liquid form) is encased in a glass tube. The thermometer is marked with numbered degrees, which represent measurements of temperature. When Hans was first designing his invention, his subword sense informed him of the word "thermometer" being used on Earth, and also that the word for the units of measurement was "degree." After a bit of thought, the subword sense also made him realize the word degree could be used for other purposes (such as cartography, though this usage of "degree" wouldn't happen on The Land until 885).
His subword sense failed to inform him of any particular words for distinguishing degrees of temperature from other types of degrees, so for this he sought the advice of a spirit-talker, who asked a spirit about the matter. The spirit mentioned several different scales used on Earth for measuring temperature, most if not all of which were named after the scientist who had developed them. Hans didn't want to use the names of any Terran scientists, but he didn't want to use his own name, either. And so, he decided it would make the most sense to simply call them "degrees Thermal," with the symbol being °T. As it happened, one Terran scale, Celsius, used the method Hans had himself chosen for designating degrees: The freezing point of water would be set as 0°T, and the boiling point would be 100°T. So, the space between these temperatures would be divided into 100 equal units.
Prior to the invention of the thermometer, Landians rarely gave much thought about temperature, finding it sufficient just to say "hot," "warm," "cool," or "cold." However, in the years to come, the measurement of temperature would become useful for various purposes, used by weather prophets, cooks, farmers, physicians, chemists, and any number of other professions. Thermometers are of course also commonly used by anyone to keep track of the weather on their own, though this is more common in the villages of the Northern Alliance than in most other villages on the Land.