198 



The Kata-thermometer as a Measure of Ventilation. 

 By Leonard Hill, F.R.S., H. M. Vernon and D. Hargood-Ash. 



(Received August 20, 1921.) 



(From the National Institute for Medical Research, Hampstead.) 



In two papers previously published, one by Leonard Hill, 0. W. Griffiths 

 and M. Flack,* and the other by Leonard Hill and D. Hargood-Ash,f the kata- 

 thermometer was described in detail, and formulae were given connecting the 

 heat loss with temperature, wind velocity and vapour pressure. Various 

 discrepancies were found to occur, however, and seeing that the kata-thermo- 

 meter has become recognised as a measure of ventilation the whole matter has 

 now been carefully reinvestigated. Large wind tunnels such as those at the 

 National Physical Laboratory, which were not available during the war, owing 

 to the urgency of aeroplane work, were now at our disposal. 



Experimental Work. 



To obtain known wind velocities for the experimetal work two methods 

 were adopted, that of the " wind tunnel " where the air is drawn through a 

 long tunnel by means of a propeller at one end, and that of the " whirling 

 arm " where the " kata " is made to move through the air on a revolving arm. 

 The wind tunnel work was carried out in the engineering department at the 

 National Physical Laboratory by kind permission of Dr. T. E. Stanton, where 

 Miss D. Marshall gave us valuable assistance in the determination of wind 

 velocities ; also at East Loudon College, where Dr. N. A. V. Piercy was good 

 enough to allow us the use of the tunnel and to help us in determining the 

 wind velocities. 



Observations with the whirling arm method were taken at the Physiological 

 Laboratory, Oxford, and at the National Institute for Medical Research, 

 Hampstead. The observations at Oxford were made: (i) in a large room, all 

 the doors and windows of which were closed, and air currents were further 

 reduced by surrounding three sides of the table on which the apparatus stood 

 by screens covered with several thicknesses of brown paper. The fourth side 

 had to be left open, so as to admit of light, and of a point from which to view 

 the " kata." Air draught from below was prevented by means of horizontal 

 screens placed on the table supporting the apparatus. A moving air current 

 of known velocity was obtained by clamping the " kata " to a brass rod fixed 



* ' Phil. Trans.,' B, vol. 207, pp. 183-220 (1916). 

 t ' Eoy. Soc. Proc.,' B, vol. 90, pp. 438-447 (1919). 



