438 



On the Cooling and Evap07'ative Powers of the Atmosphere, as 

 Determined hy the Kata-thermometer. 

 By Leonard Hill, F.E.S., and D. Hargood-Ash. 

 (Department of Applied Physiology, Medical Research Committee.) 

 (Received December S, 1918.) 



Part I. — Cooling Power in Moving Air. The Kata-thermometer as an 



Anemometer. 



In a paper published in ' Phil. Trans.' (B, vol. 207, 1916, pp. 183-220) 

 by L. Hill, 0. W. Griffiths, and M, Flack, there was detailed the theory and 

 use of an instrument, the kata-thermometer, a large-bulbed alcohol thermo- 

 meter, for determining the cooling power of the atmosphere on a surface at 

 body temperature. A formula K/O = 0-27 -\-0'SQ^/Y, where H = heat lost 

 in mille-calories per square centimetre per second, = (3Q'5 — t)° C, where 

 t = temperature of enclosure, and V = velocity of air current in metres per 

 second, was obtained for the lo§s of heat of the dry kata-thermometer in a 

 current of air ; 36-5° C. was chosen as the skin temperature. This is a 

 variable, and only reaches that figure in warm atmospheres. 



The constant 0'3.6 in the above formula was determined from experiments 

 which were carried out with the apparatus then available in a tube of which 

 the cross-section area was of the same order of magnitude as that of the 

 kata. Therefore, in calculating the velocity of the air current, i.e,, the mean 

 velocity of the air striking the kata, the area of cross-section of the kata was 

 subtracted from that of the tube. . 



In later experiments the authorities of the East London College have been 

 good enough to allow us the use of the large wind tunnel and other smaller 

 tunnels established for aeroplane observations. Mr. N. A. V. Piercy, the 

 lecturer on Aeronautical Engineering, has kindly helped us to determine 

 very exactly the velocity of the wind in the tunnels. 



In all three tunnels used the air was drawn through the tunnel by means 

 of a large electric fan, and the velocity deduced from the difference of pres- 

 sure inside and outside the tunnel, the gauges used being calibrated by 

 means of a Pitot tube. All the tunnels were of square cross-section. The 

 largest tunnel used was 48 inches wide and made of steel. The pressure 

 difference was read from tilted gauges, the velocity being given by the 

 formula : — 



where V is the velocity in metres per second, K a constant depending upon 



