444 



Prof. L. Hill and Mr. D. Hargood-Ash. 



/ or V from wet kata readings, but it does allow us to determine approxi- 

 mately from kuown data of / and V given in meteorological records, what 

 would be the evaporative cooling power. We only propose to use it for that 

 purpose. Using in addition to the ordinary kata one calibrated from 90° to 

 75° F., and another from 110° to 130° F., we investigated the effect of the 

 surface temperature on the evaporative power. Graph III gives the results 

 we obtained in two of our experiments carried out at different air tempera- 

 tures and vapour tensions. In one ease the evaporative power increases 

 from 7 to 34, a difference of 27. In the other case from 15'5 to 44 5, a 



50| — — 1 1 1 1 1 1 1 1 1 — ■ — I 1 \ I I I r 



I 11 I 11 I I L_ i I L_ 1_ 1-5 U U K 



20°C. 22° 2? 26° 2S° 30° 3? 3^ 36° 38 40° A2° 44?* 46 48° 50 5 2 54 56 56 

 Mean Temperature of Range of Cooling. 



difference of 29. The mean surface temperature increasing in each case from 

 28° to 53° C. It follows that not only in evaporation from the skin but in 

 the drying of materials the surface temperature is of great importance. By 

 means of the kata the evaporative power of drying chambers can be investi- 

 gated and drying processes made exact in place of being empirical. 



Part III. — luffed of Barometric Pressure on the Cooling Power. 



In the Eoyal Society paper cited above, the question of the effect of 

 barometric pressure on the cooling rate of the kata was briefly considered, 

 and a formula expressing the effect put forward, viz., 



H = Q^p, 



where p = the pressure and C is a constant at constant values of kata bulb, 

 and enclosure temperatures, and H applies only to cooling by convection. 



Then ^=i^. 



H p 



