From AMS Glossary
A type of cooling-power anemometer based upon the principle that the time constant of a thermometer is a function of its ventilation.
The form developed in the early nineteenth century consisted of a liquid-in-glass thermometer having two calibration markers on the stem corresponding to 38.5° and 35°C. The thermometer was heated to 40°C, and the time required for the column to fall from 38° to 35°C was measured by a stopwatch and used to compute the wind speed. It was especially useful for very low wind speeds. The katathermometer was used also, in human bioclimatology, to determine cooling power.