206 The Kata-thermometer as a Measure of Ventilation. 



between the heat loss and the surrounding conditions, and that this relation 

 may be expressed in the form 



H = (a + ly/v)0 



for the dry " kata," where H is the heat loss per second per square centimetre 

 of " kata " bulb surface, 6 being the difference between 36 - 5° C. and the dry- 

 bulb temperature, and v the wind velocity in metres per second. The equation 

 takes the following numerical forms for air velocities above and below 1 metre 

 per second : 



H = (013 + 0-47 v 'v) 6 (ii) and H = (0-20 + 040 y/v) 6. (iii) 



The wet "kata" formulae are more complex (see p. 201), but for ordinary 

 atmospheric temperatures and humidities an approximation is yielded by the 

 formula 



H' = (p' + Vf/v)&, 



where H' is the heat loss per second per square centimetre of wet " kata " 

 bulb surface, and 6' is the difference between 36 - 5° C. and the wet bulb 

 temperature. 



This equation takes the following numerical forms for air velocities above 

 and below 1 metre per second, 



H' = (0-10 + 1-10^/' v)6' (iv) and H' = (0 - 35 + 0*85 i$/ v) 6'. (v) 



(It should be noted that the above equations are not true when v is less 

 than - 04 metre.) By means of equations (ii) and (iii) the " kata " may be used 

 as an anemometer, both for estimating wind velocities out of doors, or the 

 velocity of air currents indoors for purposes of ventilation. For the latter 

 purpose it has a special value, for it estimates cooling effects of air currents 

 whether unidirectional or eddying. 



