Section III, 1920 17] Trans. R.S.C. 



Anemometric Tests with the Kata Thermometer 



By L. H. Nichols, B.A. 



(Presented by Dr. A. S. Eve, F.R.S., F.R.S.C.) 



(Read May Meeting, 1920) 



(Summary) 



The Kata Thermometer^ as designed by Dr. Leonard Hill and 

 used for the determination of the cooling and evaporative powers of 

 the atmosphere, consists of a large cylindrical bulb and a stem grad- 

 uated from 95° to 100°F. The heat loss from the buJb in millicalories 

 per square centimeter per second at its average temperature can be 

 determined by dividing the time of cooling into a calibration factor 

 for the instrument. 



The great value and accuracy of the instrument under indoor 

 conditions have been satisfactorily confirmed by many independent 

 observers, but for outdoor work certain unexplained variations have 

 reduced considerably the limits of the precision obtainable. 



It is important to note therefore that the object of the anemo- 

 metric tests is not so much to demonstrate its rather limited applica- 

 tion as an anemometer as to check the theory of the instrument 

 under practical conditions where the air circulation is rapid and 

 irregular, and the incident radiation uncertain. 



At the suggestion and with the advice of Dr. A. N. Shaw of McGill 

 University, the writer has made a series of trials with the dry bulb used 

 as an anemometer in the open air. These tests consisted of com- 

 parisons with three standardized anemometers, the Robinson Cup, 

 the Hicks Turbine, and the Pitot Tube. The accuracy of observation 

 and sensitiveness to gustiness of the two former instruments were 

 greatly increased by improved recording mechanisms. 



The Kata Thermometer has indicated values for wind velocities 

 which were in some cases as much as 60 per cent greater than the 

 average of those obtained by the standard anemometers mentioned. 

 An analysis of the results on many different days confirms the fact 

 that gustiness and radiation from the surroundings have a marked 

 effect which varies with the conditions. 



1 Hill, Griffith and Flack, "The Measurement of the Rate of Heat-loss at Body 

 Temperature by Convection, Radiation, and Evaporation." Phil. Trans .Roy. Soc, 

 B.. Vol. 207, p. 201 (1915). 



Hill, F., and Hargood-Ash, D., "On the Cooling and Evaporative Powers of 

 the Atmosphere as Determined by the Kata-Thermometer." Proc. Roy. Soc, B., 

 Vol. 90, pp. 438-447 {1919). 



