THE ROYAL SOCIETY OF CANADA 



/•a 



■7 



70 



2.0 



30 



4-0 



SO 



to 70 , 



V IT7 TTîZs per fi r 



Flq. 3 



This comparison thus shows that the records given by the Cana- 

 dian anemometer are too high for velocities above 15 miles per hour 

 and that for higher velocities they should be corrected by means of 

 the equation 



Y = 1-24- -25 logV 

 or the correct values can be obtained directly from 

 V'^ = y V = V(l-24-.25 1ogV) 

 where V is the corrected velocity and V the recorded; Marvin's 

 equation can also be used. 



Relation Between the Most Probable Gust Velocity and the 

 Mean Hourly Wind Velocity 



The pressure tube anemometer by its construction gives a graphic 

 representation of the actual character of the wind, showing the gusts 

 and the lulls, and, at the same time, permits the determination of 

 the mean velocity of the wind. It is thus possible to determine the 

 mean velocity during a given interval and the highest and lowest 

 velocities that occurred during that interval. The exception to this 

 is when the gusts or lulls are of such short duration that the recording 

 part has not time to follow the pressure changes in the wind. On the 

 other hand, the cup anemometer gives the mean velocity during an 

 interval but not the highest or lowest velocities occurring during that 

 interval. If, however, a relationship between the maximum velocity 

 and the mean velocity as given by the pressure tube anemometer can 

 be determined, then this relationship can be used to determine the 

 highest maximum velocity from the mean velocity of the cup ane- 

 mometer. 



