Fahrenheit reference points became popular following the work of Anders Celsius and these fixed points were adopted by a committee of the Royal Society led by Henry Cavendish in 1776. Under this system, the Fahrenheit scale is redefined slightly so that the freezing point of water is exactly 32 °F, and the boiling point is exactly 212 °F or 180 degrees higher. It is for this reason that normal human body temperature is approximately 98° (oral temperature) on the revised scale (whereas it was 90° on Fahrenheit's multiplication of Rømer, and 96° on his original scale). The Rankine temperature scale was
Lava River Cave this section of the cave requires visitors to crawl on hands and knees for much of the distance to the cave’s end, and usually takes at least thirty minutes. The air temperature at the mouth of the cave ranges from about 32 degrees to around 45 degrees Fahrenheit (-1 degrees to around 7 degrees Celsius) depending on the time of year. Inside the cave, it is a constant 42 degrees (5.6 degrees Celsius). As a result, the Forest Service strongly recommends that visitors wear a warm jacket while exploring the cave. Lanterns can be rented at the visitor center above