200 Prof. L. Hill, Messrs. H. M. Vernon, and D. Hargood-Ash. 



Each point in these graphs is the mean value obtained from three to seven 

 observations of cooling, taken consecutively. Where points coincide the 

 observations were taken at different times. Several kata-thermometers were 

 used, the factors in each case being verified. The high velocity observations 

 were taken in the wind tunnels and the low velocity ones by the whirling 

 arm method. Unfortunately, owing to experimental difficulties, it was not 

 found possible to make these two methods overlap, the lowest wind tunnel 

 velocity available being 3'05 metres per second, and the highest whirling arm 

 velocity for the dry " kata " 1/77 metres per second. 



~No equation of the above form will apply for all velocities over the range 



Velocity - Metres per second 

 Fig. 1. 



tested, but from the value y/v = 1 to y/v = 42, that is, between the velocities 

 1 metre per second and 17 metres per second, a curve may be drawn to fit the 

 points as shown, the equation of which is 



H = (013 + 0-47 vA>) . 6. (i) 



It should be noted that the above limits include observations in air currents 

 obtained by both methods. Below 1 metre per second velocity another curve 

 may be drawn, of which the equation is 



H = (0-20 + 0-40 y/v) . 0. (ii) 



