Wet Bulb Temperature and Climatology

Abstract

IT is rather disappointing to find, according to your report of the proceedings of the Section of Physiology of the British Association, the discussion upon climate had to be abandoned because no one was prepared to follow up Prof. Osborne's contribution to it. For the points raised by Prof. Osborne, according to what we gather from your short report (p. 322), are of great and vital interest. He emphasises the importance of the readings of the wet-bulb thermometer as indications of what one might call the evaporative quality of the atmosphere as it affects the economy of the human body. Unfortunately the wet-bulb thermometer is untrustworthy for several reasons, and it is well known that physicists treat it with scant respect. Its indications depend in an uncertain way on the physical condition of the air surrounding it, and no one has been able to give a satisfactory method of deducing from its readings the value of the vapour pressure of the atmosphere. Recent experiments of ours with the Kata thermometer prove beyond question that the rate of evaporation from the skin depends directly on the defect of the actual vapour pressure in the surrounding air from the vapour pressure in contact with the skin, and the value of the air vapour pressure can be determined very easily by means of a couple of readings of the dry and wet Kata thermometer.