The Kata-tliermometer as a Measure of Ventilation. 201 



These two lines are shown with the experimental points as the lower curves 

 in the diagrams. 



0-1 0-2 0-3 0-4 0-5 0-6 07 08 0-9 1-0 



Velocity-Metres per second 



Fig. 2. 



The Wet "Kata" — Wind Velocity, Temperature, and Evaporation. 

 Wet " kata " observations were made in a similar manner to the dry " kata " 

 ones, except that the bulb of the instrument was covered with a muslin 

 " finger," which remained moist during the time of cooling. In this case a 

 velocity as high as 2'50 metres per second was obtained by the whirling arm 

 method. With the wet " kata " heat is lost by the evaporation which takes 

 place in addition to the heat lost by convection and radiation, as in the dry 

 " kata," so that the wet cooling power, H', is always greater than the dry 

 cooling power, H. It is evident, then, that in addition to the temperature 

 and wind velocities, some term must be introduced to take account of the 

 humidity of the air. In the ' Phil. Trans.' paper the formula deduced from 

 theory and experiment was of the form 



H' = (a + b y/v) 9 + (c + d ^v) (F -f)W 



VOL. XCIII. — B. Q 



