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



If the kata is used to determine the cooling power under ordinary con- 

 ditions of wind and temperature, the loss of heat is obtained by dividing the 

 kata factor by the time of cooling, hence the formula H/^ = 0*27 + 0'49.^/V 

 does not enter into the calculation. To deduce the wind velocity from the 

 cooling power, however, the above formula is used, and an error not exceed- 

 ing + 12 per cent, may occur in the result, this error being due to the varia- 

 tion of the constant discussed above. For example, if the velocity given by 

 the kata is 2"5 metres per second, then the true velocity will lie between 

 2"2 and 2"8 metres per second. Similarly, in calculating kata cooling powers 

 from temperature and wind velocity data published in the meteorological 

 reports, errors of the same magnitude may come in. 



Table 2. — Values Obtained from Experiments in Wind Tunnels. 



H. 



9. 



Velocity. 



H/e. 



35 -6 



17 -0 



13 -8 



2-09 



39 -6 



19-7 



12 -2 



2-01 



37 -9 



19-4 



12 -2 



1 -95 



33 1 



17-0 



11-7 



1-93 



35 -2 



19 -4 



10 -4 



1 -81 



35 -2 



19 -8 



9-05 



1 -78 



33-2 



19-4 



8-5 



1-71 



32 -0 



19 -6 



7-4 



1-63 



31 1 



20 -0 



6-8 



1 -55 



31-5 



19 -7 



6-7 



1 -60 



31 -3 



19-6 



6-7 



1-59 



30-2 



19 -4 



6-5 



1 -56 



31 -6 



20 -5 



6-5 



1 -53 



31 -3 



19 -7 



6-3 



1-59 



28 -9 



19-6 



6-2 



1 -47 



27 -9 



19 -5 



5-4 



1-43 



26 



19 -5 



5-0 



1-33 



21 -4 



19 -5 



3-2 



1 -10 



19 -7 



19 -4 



2-8 



1 -02 



Part II. — Evaporative Power in Moving Air. 



Having re-determined the formula for the dry kata in moving air, it 

 became necessary to re-investigate the formula for the cooling of the wet 

 kata in moving air, which was provisionally given in the Eoyal Society paper 

 cited above. 



It was not possible to use the large wind tunnels for any extensive investi- 

 gation of the wet kata, because these tunnels are placed in very large halls, 

 the temperature and humidity of the atmosphere of which we could not vary 

 at will. After taking some preliminary observations in these tunnels, which 

 gave us indications for the construction of the new formula, we employed a 

 tube 4 feet long and 3 inches in diameter, and a fan which sucked air 



