The Cooling and Evaporative Powers of the Atmosphere. 4^1 



It must be borne in mind that the kata must be shaded from the sun's rays, 

 direct or reflected, when used as an anemometer. The kata shows the effect 

 of eddies and air movements which are too small to affect cup or fan 

 anemometers. This gives it an especial value in the investigation of the 

 A'^entilation of rooms. 



As shown in the paper cited above, there is a limiting velocity value 

 beyond which the kata no longer follows the formula. 



With respect to the observations detailed in Table 2, a certain amount 

 of variation was found in the values obtained for the constant, the mean 

 value as given by the graph being 049. This variation may be due to 

 (a) experimental errors of observation, (h) errors due to causes the effect of 

 which could not be determined. In this latter class would be included errors 

 due to the fact that the kata, being a very sensitive instrument, detects a 

 slight change in temperature or velocity before it is shown by thermometer 

 or pressure gauge. Errors due to radiant heat, alteration of pressure, or to 

 changes in the glass and liquid of the instrument must also be included in 

 class (&). For example, it was found that the temperature of the water in 

 which the kata was heated had a slight effect on the cooling power, this 

 being greater when the water was at a temperature of 80° C. than when it 

 was 45° C. Water in a Thermos flask at about 80° C. should he used for all 

 kata observations. 



•OS - 



-on l 1 I I I I I I I I I I I i 1 1 1 1 



1234-56789 



Wind Velocitv, metres per second. 



In this connection it may be noted that the first of a series of observations 

 of cooling of the kata is not reliable and should be neglected. Since errors 

 under class (a) would be eliminated by taking the mean of a number of 

 observations (as was done), it would appear that the variation in the constant 

 must bo due to undetermined causes. This is also pointed to by the fact that 

 observations taken on any one day gave constant values. 



