96 THE ROYAL SOCIETY OF CANADA 



2. The actual velocity can be obtained from the recorded velocity 

 by means of the equation 



Va = Vr (l-24--25 1ogVr) 

 where Va is the actual velocity and Vr the recorded velocity. 



This equation is practically identical with Marvin's equation 

 Log V= -509+ -9012 log v 

 where V is the actual velocity and v the velocity of the cup centres. 



3. The most probable velocity in a gust can be obtained from the 

 equation 



Vg = 3 + l-26Vm (a) 



or from Simpson's equation 



Vg=l-5 + l-3Vm 

 where Vg is the gust velocity and Vm the mean hourly velocity. 



4. The possible extreme velocity that may occur in a gust would 

 appear to be 



Vg=14+l-26Vm (Ô) 



or 



Vg = 3 + l-64Vm (c) 



5. Equations (a), {b) and (c) when applied to the Canadian 

 Standard Anemometer may be put in the form 



Vg= 3+Vr (1-56- -315 log Vr) (a) 



Vg=14+Vr (1-56 --315 log Vr) (6) 



Vg- 3+Vr (2-04-.41 log Vr) (c) 



Marvin's equation 



LogV= • 509+ -9012 log V 

 was obtained from the results of experiments on a whirling arm cor- 

 rected to open air conditions and the results agree so closely with those 

 obtained at Toronto by an entirely different method that there can 

 be no doubt about the velocity given by the standard anemometer 

 in use in the United States and Canada being much too high for the 

 higher velocities. The results in both cases were obtained from ob- 

 servations of winds under 35 miles per hour, and to determine the cor- 

 rection accurately for high velocities it will be necessary to make the 

 investigation where high winds are of frequent occurrence. These 

 conditions can be obtained at some of the Atlantic coast stations, but 

 it cannot be done until after the war. 



The Meteorological Office, . 

 Toronto. 



September 1st, 1916. 



